I've made more progress! I'm well into Friday's "The Abyss" and have decided to take a breather.
Impressions of contributed areas:
The introduction seems a bit lackluster compared to EK2. There's no title screen, for instance. Slime Fields was a clever beginning area, though, and I had a lot of fun in the Climb Ruins.
I barely remember the Cave of Robots but I guess that means I liked it?
Obviously Hospital Innerspace was the best area in the game and is perfect in every way. The Magic Rocketship Adventure was one of my favorites, as well.
Condemned City had really excellent aesthetics and storyhaving, but in the second half, Friday, if you're going to use a SFX channel instead of a music one in order to make sure the music loops, please pick a version of the song that actually loops instead of fading out!
The Save Area looked great but I wish it had more going on in it.
I did not like The Wall very much. I found it far too difficult and not very interesting to look at or listen to.
The Mine of the Golden Key had very impressive scripting and puzzling, and is one of my favorite of Kazz' areas, but I must mention that I noticed the assembly of the level had a few graphical seams in it (mismatched edge tiles, use of Sign instead of contiguous Sign Area blocks, etc.).
The White Pyramid was a lot of fun, but [spoiler]I think I enjoyed the obstacle rooms more than the things I played in order to retain the keys that allowed me to skip them. Still, the option to skip them, which I did exercise on occasion, was much appreciated, and I also enjoyed the reward for making it through with both the blue and the purple key[/spoiler].
So that's where I am so far.