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MAP21 - Base Stimpack by Charcola
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Welcome back to Doom mapping! Interesting decision at the start, where you go into the obvious secret and then have to choose between the two weapons, the other one being unexpectedly blocked off. If I hadn't chosen the chaingun I don't know how I'd have made it through this map, though.
The map design is very flat and the Baron room is uninteresting - he's just hanging around facing the other way with some rockets scattered about! But it improves once you go beyond the red door, it seems you had got back into the swing of more interesting spaces again by then

Like I mentioned in another reaction, I'd recommend against swapping the SW2->SW1 textures without good reason, because it makes it far less obvious what you've activated and what you haven't.
Oh come on, a Cyberdemon when I'm armed with a twig and the contents of my packed lunch? Not touching that!
Beautifully executed delayed trap with the switches in the blue area

The first is an obvious trap that appears to just give you ammunition... then the real trap begins

At this point the level suddenly becomes a lot more interesting, with more varied scenery, a complex series of buttons and switches to get to the Super Shotgun secret...
...and I take back what I said about the Cyberdemon

What a great moment of dread, to have him suddenly gone and looking around to find him!
I'm beginning to see what the map's drawing out now! That's creative.
Vast array of rockets on the ground can only mean one thing... and yes, there he is. All the rockets and most of the plasma later, the map's over...
...but that's a nice gesture, giving the automap at the end so you can go back and see what you've missed. I like the little room that's opened up at the start, but you can get stuck behind the yellow key pedestal.
That was good! It started off basic but noticeably improved as you went.
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MAP22 - Crunk Refinery by BobBarker
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Expert map! But this is something a bit different, which is nice - it's decorated a bit differently from most maps with the new variants on the classic textures.
The yellow door doesn't need a yellow key! I'll close that up anyway and find it before I go through there...
(A while of wandering around later...) I think I was wrong and this was intentional - the yellow key trim indicates the door where you get the yellow key, not the one where you use it? That seems like an objectively bad choice.
The end is also a bit of an anticlimax - just wandering over to the red door which isn't even very significant, and pulling the switch to exit - but the map is otherwise great. I love the little messages everywhere, giving a sense of progress in a large sprawling map.
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MAP23 - 0-Pipe Gear by Toooooasty
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Okay, this would be one of those Quake 2 maps I was talking about

Great use of moving sectors and architecture for the various machinery, it looks great and varied throughout and the icy boss room was a nice change of scenery. I had a problem with a multitude of imps spawning on top of each other on the top of the barrier to the east of the conveyor room (I think), and I thought the jump from the first tall room to get on to the girders and make your way into the room with the pool was too awkward - but it's possible I did it wrong and didn't notice the intended solution.
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MAP24 - Escape from Argent Prison by Lance Charleson
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Interesting start... I'm not entirely sure what I did to escape the cage? I thought I was going to have to wake the enemies up and get them to accidentally open it in the crossfire or something, but is it pushing on the back side of the blue panel with the switch? Getting the blue key right off the bat is a bit unusual, the blue doors might as well not be there at all.
The scenery's good, though - the pillars and walls of the prison itself, and the way the open skybox frames it all, and you use fog well and lead the player through a couple of different challenges. Having the super shotgun right in front of your eyes and not being able to pick it up is an unnecessary tease
The pink demons in the sunken floor in the third section are a bit easy because there's no way for them to climb up to you!
The tower looks really great and imposing, looming in the fog outside the prison - but you have to turn around and go back to see it! Getting the player to face some structures like that naturally would make sure the effort isn't wasted
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MAP25 - Live Fire Exorcise by Sgt. Shivers
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That title is either a misspelling or a mighty pun

I'm looking forward to seeing where this goes!
That definitely immersed me! It's a clever way of putting the Portal puzzle approach into Doom, making it about trying to get line-of-sight to switches and working out your most efficient route to get through the room before the door closes. I was impressed that you included the escape (although there was a lack of health) - and the pile of monsters at the end was an unimaginative conclusion to an otherwise very innovative level
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MAP26 - Attack First by Simpletonn
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Nice dark start

And the vent secret is interesting in that you can poke your head into a later room and make it easier for yourself when you get there.
This is another map where I'd recommend setting the doors back into frames so that they're not flush with the walls and appearing to slide into the ceiling. It would also be good to have a reason why we can't open the last door in the hub.
The route around to the red key is a little... tiny - you could had done more with that dark computer corridor

Make sure to align your textures horizontally, too, as some of them were cut off. The next couple of rooms are good as you get more ambitious with a split-level room and the bridges over the rails. I'm not a huge fan of invisible walls - if the player wants to drop down and electrocute themselves it should be on them
The third secret is just an alcove in the outdoor area that doesn't do anything! Was that a mistake? But you're getting into more advanced stuff now, with the teleporting Revenant.
This is a good starting map, it falls into some traps but it's well put together

Overall most of the rooms are a bit too big and empty for their own good and could have done with some tightening and decoration to spruce them up - you have a go at it with the crates and the cylinders in one room near the end, which stood out as good. And there's a bit of backtracking when you get the last key, which you could have made more interesting by adding more enemies as the player makes their way back - or provided an alternative route to get out that circles you around back to the hub. Either of those would have given the plasma gun you get at the end more reason to exist
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MAP27 - Hitler's Prison by Luigi2600
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Starting off being shot from all sides! The skybox is interesting, makes it look strangely oppressive. You can shoot through the glass/force field, is that intentional?
The blue door has no indication that it's a blue door visually - this isn't a huge problem in such a small map but it's a nicety that the player will be used to.
The man himself doesn't seem to... do much and isn't counted as an enemy? But I got an "invalid ACS module" error on level start, so that might have something to do with it.
I think you've got the starting basics covered here - laying a playable map out, using doors, and the technique of breaking large expanses of wall up with other textures. In your next map, try adding things like moving lifts, more use of multi-level rooms, and so on!
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MAP28 - Tomb of Hectikhamen by Action Max
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Great use of textures from the start, although they bring back terrible flashbacks of Hexen II! The traps are creative and notable for being near-weaponless, the only time heavy use of firepower is required being the fight with the barons on the tightrope with the rocket launcher. I felt you could have done more with the Spiderdemon room, it seemed like the Revenant up there was a bit of an afterthought.
There's a missing texture on the lower left of the crusher above the Spiderdemon, only obvious when the crusher is down. And while it's short and not very detailed, the strength of this map is its willingness to experiment with something different.
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MAP29 - The Weed Number by Abysswalker
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I'm the only person in the western world who hasn't played Dark Souls, so the meaning of the quote is lost on me - I wonder what that means?
Oh. Okay, I think I can guess now. The first room is full of sudden traps and unexpected teleportation, though you ease back on it a bit later on (which is nice). The rooms are distinct and have enough character to them - jumping puzzles in Doom are always a bit awkward but the pillar jumping works well enough.
One of the Zombiemen on the curved stairs is trapped in the wall.
Oh, come off it with your double Archvile fight! I don't have the ammunition for that.
The room behind the red door is nice - but you can walk through the bars of the Baron's cage! I would also probably have removed the cramped little space to the right of the door where the top platform doesn't meet the wall.
The super shotgun is well placed, it feels like a reward as well as a great boost going into the fight with the Baron.
You could have put in some more monsters on the route back from the red door to the yellow one.
Hopping about in the slime now... the Megasphere is appreciated but it's really a bit much!
The viney walls around where you get the bonus ammunition in the slime river are a bit thin between the alcoves, they look like they're made of paper.
Nice trap leading to the end

I was looking around for where the ambush was going to come from and I didn't expect the way that it played out!
The map crashes at the end but I think it's really crashing at the start of going back to the hub (GZDOOM g2.1.1). This was a decent map

The balance was off in places but it had a good variety of challenges, not staying on the same thing for too long.
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MAP30 - This is Serious Now by Deathzor
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What's the weather like today? It's FIREBLU.
You keep things moving along nicely so far, but the rooms are all big and plain - some decoration or shrinking them down would help, I feel. The library feels about right.
The moment when you step out the door to the outside again and realize the expanse of the level is good - I would perhaps have liked that to be more dramatic! Get your first glimpse from an upstairs balcony somewhere...
There are a few too many big enemies for the arsenal available just now (around the end of the first walkway entering the tower), I've been plugging away at Knights for a while...
...and Barons in the later building! Fortunately the Super Shotgun comes to the rescue here.
It's about here that I noticed how much this map lets you see areas you've been in before or areas you'll visit later, from different vantage points - that helps a lot with the flow of the map and making it feel like a cohesive whole.
The caves section later on has a teleport to escape the lava but it doesn't work! The elevator at the end of that doesn't look like a texture that you can activate, either - that would be better realized as a switch, I think.
After playing the rest of this level, I think my thoughts can be summed up better in one paragraph... while it's impressive that you managed to put such a long level together in the time constraints, I think the length ends up working against the map. It's a level with slightly too much of everything - too many meat walls at the start, too many demons charging at you in corridors to be lazily chainsawed through, and too many encounters that teleport enemies in and add 50 or so to the monster count. I'm pretty sure the count had doubled from an already fairly high figure by the time I'd finished the level, and it fatigues the player, moving the goalposts of finishing the level further and further away. The Archvile after the final boss was just insulting

The amount of detailing also suffered a bit due to the vast expanse of the map, with a lot of plain-looking flat rooms among a few nice ones.
I definitely appreciate the amount of effort that went into this one, though!