I got to Shadowlands... There, the game really gives you problems.
As of earlier levels, me personally I would remove half of Mystic Ambits and some of the health items from levels 02 to 07, to make things challenging.
Also the track in Water Temple is reeeeeeeeaaaally annoying, and being fast and loud, makes you want to turn the music volume in game down, which I did... Maybe you could edit this track to make its volume lower by default? Or just replace 'cause honestly I have no idea how it connects to the Hexen atmosphere (other tracks that I've come across as for now, fit perfectly).
Now about the things I love in this wad.
First of all, its own unique style. With narratives, exit doors and cutscenes. It's a bit odd first, but when you get the theme after 1-2 levels, it's very cool.
To own unique style also - instant kill lava, lol. First i was like "oh what the..."

, but then it seems really a part of style too.
Next, monster placement and level design. First level is a gem. Being realistic and highly worked location, it places monsters in such a way that they present danger to you, especially those serpents. Ettins and stalkers in the dark are cool too, especially that sense of lurking unknown in the dark. Drathi Marshes is good in making a "no place to feel safe" atmosphere (though Fire Canyon is better at it, lol, with no real possibility to conveniently kill fire stalkers, because you know, they live in friggin instakill lava

). Drathi Canyon is good at monster spam and at the same time is a highly atmospheric location. That is where I most wished that the game hadn't given you 20 armor class - those battles would be awesome if they were just a wee bit more dangerous. Same goes to the heresiarch battle at the end of hub.
I really liked the water puzzle in the temple.

Again, the sub-levels of the Valley of Rateshk hub are the ones when you start feeling problems, so their design is perfect to my opinion. I can't name the things I don't like there, I love absolutely everything. %)
And maybe to someone key/switch hunt in Town of Jualtsa was too boring, but I think this is cool and realistic, you search for a friggin key in a big town. I liked it where the steel key was at, very good moment

I like it that the levels don't seem monotonous and always offer you something new.
P.S.: just noticed:
Caleb13 wrote:-First 6 maps (or so) are disproportionately easy compared to what comes later on.
If you don't believe me, believe this man, he made Masters of Chaos for Heretic, he knows about balance! (MoC is perfect in sense of balance)
