I thought this was quite good for a beginner's effort, and I wouldn't have considered it bad at all had it been done by an experienced mapper either. I played through it on Hurt Me Plenty and didn't have any problems with ammo or health. In fact I think the health is somewhat overabundant. There were loads of medikits and stimpacks that I didn't need, and I don't think playing on UV would have made much of a difference there. I had a good amount of surplus bullets, but those are probably needed on UV, so I would guess it's not a problem.
I noticed that all the little health and armour pickups scattered about on the crates always had little "stairs" leading up to them, so I was unsure if I was allowed to jump, although in hindsight it doesn't look like it would matter if I did.
There's a lot of detail in the map, although sometimes I think it's a little too excessive. I think some of the rooms could look better with a bit less, more tastefully applied, detail. But overall it was quite pleasing to
look at. The shadow monsters seemed to fit in well, although I'm not sure if those green imps at the end ere supposed to be some sort of "mini boss battle", because they were easily disposed of. I'd suggest to replace them with a larger group of normal imps and save the green imps for the next level, as they felt a bit out of place with just two of them near the end of the level. They seem more suited for being used throughout a level rather than as an "end battle", due to how weak they are. The finish was rather anticlimactic because of this, and perhaps a regular Imp ambush near the exit would be more interesting. Say when you attempt to open the exit, walls on either side open and Imps are upon you. In one of the openings a switch would open the exit door.
Speaking of the exit, an exit sign would be cool so it's clear that it's the exit. A player might accidently walk into the small exit room without realising it's an exit, which would be annoying if he'd planned on searching the level for any missed secrets or other stuff before leaving. And speaking of secrets, I wouldn't have minded maybe one or two extra, minor secrets. The secret in the room with the red Duke button where shadows come out from three sides was also easy to spot using the automap. You can avoid this by flagging the linedef as "secret". I think the difference in the texture on the wall compared to the other two shadow closets is clue enough.
The gameplay kept me interested, so in summary I'd say it was a short and sweet level with a decent amount of eye candy.
I recorded a demo of my play through the level. I used
GZDoom 1-2-01 to record it, so you'll need to use that if you want to have a look. See attachment below for the demo file.
Looking forward to more levels from you.