Eruption Conduit Zone Act 1:
No beating around the bush, the beginning looks awful. It might just be that I don't like the RVZ texture set that much, but just compare the cave parts to the outside parts. So, I suggest trying a different set of textures (again), or at least mixing it up. You might wanna get some inspiration from Infernal Cavern and the 2.0 contest version of Magma Core. Even though both are cave levels, I think the textures could be used for outside rooms as well. The RVZ textures are probably best used for smaller details and not for huge walls. If nothing else works, try to rework the outside rooms to be less open and tall. The problem is that everything has the same dark reddish tone, so try adding some different colors to balance it out.
So, there is this half-hidden, optional path that leads along the upper sections of the level at the beginning. I actually quite like it (except for RVZWALL7, it just doesn't fit), but at the end of it, where the Star Post is, I am way too high up there, with a lone Crawla facing away from me and no clue where I am without jumping down. You should probably just end this path at the height you have at the lava fall, and not make it ascend even more. Just leave out the last row of springs and be done with it. By the way, the blandness of the RVZ texture set becomes especially apparent in the more secret, higher regions, which are quite simply put a bunch of red rock.
Apart from this, there's not much to comment on in this level. The cave sections look great, and you might have actually pulled the variation thing off better than RVZ itself. I still don't quite understand why the optional factory entrance requires an Elemental Shield, especially since there is no real path split at that point anyway. You tinkered with the light blocks, and they work well now. The factory wall on the other path at the end could probably use some additional detail, although that's not much of an issue.
Eruption Conduit Zone Act 2:
I still don't like the room where the four paths split off, and I guess I figured out why. The floating bridges look unnatural and weird, because too much of them floats and they wind around in awkward 90-degree angles. The same thing throws me off in THZ2. If they didn't wind around that much and that sharply, they'd look much better. Also, remove the arrows from the four entrances. It's perfectly easy to find the entrances, it's just a bit tricky to tell which is which. You tried adding some details to make them look distinct, but you should probably work a bit more on that. You could, for example, make each elevator look different as well. I also don't like how the turret path uses a teleporter because the conveyor gets in the way. Just shorten the conveyor and merge these paths normally.
I like what you did to the section with the sideways conveyor. I suggested to cut it off, but you did something better than that. However, if you happen to jump behind two crates just before the cave room where they paths reunite, you're stuck. Said cave room looks absolutely epic now, even though it lags quite a bit due to extensive detail. I still don't like the winding floating bridges, but it's not as noticeable here. The Crawla Commander room works very well now, and the glass-enclosed staircase is very epic. The big room after that has the same problems as the room where the four paths split. The winding platforms are ugly and annoying to navigate, especially under lag.
In conclusion, I really like this level, even if the larger factory rooms look a bit awkward. I especially like how you can view the second big room from the crusher gauntlet and vice versa. Thanks to the extremely complex layout, this level actually feels like a real factory. Again, no comment on the boss because there's nothing to say.