Maybe some inspiration from these batman mobile games:
1.)[Batman Begins]
http://spriters-resource.com/mobile_phone/batmanbegins/2.)[The Dark Knight]
http://spriters-resource.com/mobile_phone/thedarkknight/3.)[Superman and Batman]
http://spriters-resource.com/mobile_phone/superbatman/For what you have now the sprites are good. I would say to be careful about how dark Batman is compared to the BG. It looks fine right now but depending on how you render the BG it could hurt readability. Also watch out for that flaming barrel, the perspective looks more akin to RPG top down than side-view.
For the HUD, I would suggest trimming his collar because it sticks out too much and is just an oblong shape in general. Look at the faces for joker/scarecrow in that second link (Though they look painted rather than pixeled, and are much larger), it communicates a portion of their character that the small sprites can't achieve because of the res. It captures the menace of the villain, and I think if you approached it like this, a bit bigger, it would establish a similar relationship between sprite and face. I think Bane's name should be above his health bar too, and I'm guessing Batman will have a HUD on the right hand side a la fighting games?
I can imagine the tumbler would be hard to draw. Use lots of refs, maybe even make it bigger. If you do switch to SNES, you'd have more screen room to play around with, though I like the charm and rarity of cell mockups, especially when it's not something like iphone. Anyways this is pretty cool, good job, keep going. Loooved the movie.