Once again, a general thanks to everybody for the comments!
I've been a little gummed up on one section of the level (so... many... shifts...), but I wanted to send out a few more screen shots for anybody who was interested.
But first:
@Dragon MC: If you like the level enough that you want me to design something for you some time, just say the word -- countless side projects FTW!
@shawnachu: I might wind up using a couple of custom tilesets before I'm through. I don't like the look of the gray claws in the lava area from the first batch of screenshots, so I might use something custom there, and in some spots I'm finding I want bits and pieces from more than 2 tilesets, so I may make a couple of custom mash-ups.
Also, I figure it's good to share design ideas and motivations, so I wrote up an article about the reasons why I built the first few screens the way I did. It's a long article and I wouldn't fault anyone for not reading it, but if anybody is up for it and finds it useful or interesting (or useless and boring, for that matter), I'd be glad for any comments about it. The article is at my blog (linked in my sig).
Ok, on to the screens:
#1 - A straightforward but spikey jumping challenge
#2 - The east side of the summit of the mountain; this is above the entrance to ruins from the last batch of screens
#3 - The volcanic craig that explains why the ice in the previous shot is melting
#4 - Part of the broken ruins that runs through the volcanic caves