Hell yeah!
This is super inspiring stuff for sure, feedback:
ancient ruins:
Totally rad background and chars, very readable, great sand dunes and little skulls.
moonlit city:
I agree with jams that this much harder to read, took a while before i got what I was actually looking at. This might be because most of the bg is just the stripped floor, where the eye gets lost and doesn't remember the perspective. The two enemies are also very confusing and seem to defy the perspective, I don't get the at all. Nice antagonist and player with giant claws =).
abandoned warehouse:
Really nice bg, cool concrete render. Awesome explosions! I wish I could do explosions like that! Player looks good but need color for readability. Antagonist has really wierd anatomy - are the giant boobs intended?
sea bridge:
Good colors, good bg. Is the yellow thing the player? I'm also having issues with having shadow on both sides of the lower bridge. Should be only 1 px wide on one side I think.
That's my 4 cents, looking forward to seeing more!