Wow, this is a huge map. I'm going to comment on the indivudual sections and then give my final impressions at the bottom.
Prologue:
Well, it's basically the same beginning as jm_descend, the same four jumps. I like the idea of the two maps being connected and establishing the story(even though there really isn't that much to establish but still).
Part I:
First off, the surrounding area looks awful, you could've put more effort into the mountains and the lava texture(at least go for 1024x1024 so it doesn't look as repetitive). Lava moving up and down is not exactly the way fluids work but I'll let it slide because I know how hard it is to simulate fluids in CoD2. I like the textures and the jumps seem a bit on the easier side. You could've just teleported the person back to the checkpoint and not kill them. While constant deaths aren't that big of an issue here because of the easy jumps, it gets way more frustrating later on.
Part II:
'I feel really stupid just jumping down holes like this...'. This made me laugh quite a bit.

The blue chamber is quite new, I've only seen it done in one other map and I don't believe that map was released to the public(was made by Cheesy from UJ). If I'm not mistaken, you just turn the player angles upside down, right? Anyway, I liked the idea but I feel it dragged on for too long, you should've set the view back to normal after you get the blue key. In the red chamber you could've at least
put one more checkpoint in the middle but other than that, it's quite fun save for all the dying. The green chamber is the one that was the most fun for me, this hasn't been done before(at least not in that particular way) and it was perfectly paced.
Part III:
This part. This FUCKING part. I can't even begin to tell you how much I hate this part. But I'm going to anyway. First off, you have to do all of this in one go, no checkpoints in between, no splitting it up into two parts, no nothing. You just have to die over and over and over and over again until you get it perfectly done. I'm sure it's not just me, people are going to have a difficult time with this part. Seriously, how hard can it be to just make two parts on it: one when the platform is going slow and the other when it speeds up. And if you want people to do it in one go you could've at least given them three tries to do so and not kill them every time they fail. The other half of that section is a bit better, at least you don't die as much.
Part IV:
Ok the first 'CoD4' bounce is pretty cool, again I've seen it in Cheesy's map but nevermind. I wonder how you make the slippery substance, does it have something to do with the terrain patch? That's the only way I can think of accelerating that way. The second bounce is much harder. Again, why is there lava at the bottom, you could've just teleported the player back to the top...I've only done that jump once and don't plan on doing it again any time soon. The other parts with the slippery substance are way more fun, especially the small slippery pathway leading to the ladder. The accelerator was already done, again in one of Cheesy's maps.
Part V:
Getting the scuba gear is hard but as long as you memorize the pattern, it's doable. Again, why do you force people to do the same jumps over again? I found the way back more frustrating than getting the actual scuba gear. The underwater part has some kick-ass music in it, the second half(after you refill your oxygen tank) seemed much harder to me for some reason, made it with 2 seconds remaining heh. The crumbling cylinders were fun to jump across.
Part VI:
Ladder overkill? Yeah, sound about right, way too many ladders for my taste, so I basically noclipped through this part, so I can't really comment on it. Again, some kick-ass music here too! I did the part after the huge room, that was fun as well, although you really should've eased up on the ladders.
Part VII:
My favorite part of the map, incorporates most of what you had to do individually and that's what makes it fun. Again the checkpoints are a bit scarce but with persistence it's not that difficult. Except for the book jump, that one is not as easy as it seems at first glance.
Part VIII:
One of the hardest parts of the entire map. Starts off easy enough but the difficulty quickly escalates. One checkpoint per floor? Again, WHY? It never hurts to have more checkpoints, especially when it's up to the user whether he wants to use the checkpoint or not. How big is the last jump?
Part IX:
As far as boss fights go, this wasn't really a fight, per se. Pushing a giant button is hardly considered a fight.

Nice part, apart from the damn lasers before you enter the boss. Those are quite frustrating.
Conclusion:
All in all, I enjoyed the map. There are quite a few parts when killing the player is not exactly the best thing to do and could've been avoided. Sometimes the difficulty surges and sometimes it's easier than expected. Some parts could've been shortened(or rather NOT artificially lengthened->doing the same jumps to get back to your original position). The design is lacking in many places but I guess that wasn't the point of the map, for me it seemed that it was more jump oriented than design oriented. As far as sequels go, it tops the original(assuming this is a sequel to jm_descend) but could have been improved. I found the map innovative, fun and challenging. One last thing, what are the secrets for, I've only found three out of nine but I haven't found any use for them.
If you've read all of this, give yourself a cookie because this is one of the longest posts I ever posted here.
