Well, this certainly has come a long way since I last played it!
After playing through the whole game, I felt you had obviously mad a huge effort in making your levels interesting, and detailed at the same time. But....and this is quite a big but....Apart from Mineral Valley, which I though was very unique, and awesome, the rest of the pack did not 'stand out' as such.
There were certain areas in which, I thought 'Wow, this is amazing' but other times, I felt like I had seen it all before. The point I'm trying to get at is, dont be afraid to try out new things, sometimes, even crazy things to make your pack unique.
Apart from that, I loved it! There were a few smaller things too:
-In Act 1 of Zone 1, It looked as though some of the rings weren't deafed.
-In MCZ1, and parts of act 2, the lava was way too deep, or had a pit beneath it. I noticed the same problem in parts of MMZ too. It frustrates the player to fall into a pit of slime/lava, knowing there is no chance of them escaping before they die.
-In the text block of ICZ, it says 'A city set in a cold city' or something similar to it. Doesn't make sense :P
-And, Icy City on the whole wasn't the best work ever. I noticed slight references to Gloom Metropolis, which I liked, however. :) Perhaps Frozen City, or Glacier City may have sounded better, dunno, up to you I guess :)
8/10 I enjoyed it, but there's always room for improvment.
Merry christmas,
Az.