Dante's Theme - Well executed theme.
Enter the Dreamscape - Oh this is great. It gives me a very wibbly wobbly feeling. It almost reminds me a bit of the Vortex world in Sam & Max hit the road. Cool! This one is probably my favourite.
Underwater Item Shop - Definitely got that shop vibe.
Abyssal Plane - This one has a nice air of mystery as well. I like the theremin/flute-like sound.
The Nightmare Approaches - Nice ambient soundscape you got going here. It definitely builds up to something big.
Fight On! - This seems like a pretty strong tonal shift from the Nightmare Approaches. It's a really cool boss battle theme though.
Closure - It seems now that we've defeated the boss, the nightmare has turned into a dream :)
Great soundtrack!