Really cool for a concept, but I feel the character art is a bit -too- detailed for a real game. Especially since it's sprite. Not only does that high of resolution/detail mean it will take you a lot of work to animate (if you keep the detail level); but it also means your game will suck a lot of processor power and memory (especially memory) with the sprite animation and probably would have a difficult time having more than 4-5 animated {foo} on screen at a time. That said, backgrounds and statics could keep that detail level; I'd really recommend some parallax scrolling to make it come to life.
At works as an art though; mostly. Anatomy on the figuresis a little awkward in places, especially the green knights arm and both of them feel dwarven for some reason (short for their broadness); I don't know if they are actually short or if that has to do with my perception of their hips compared to their necks. Shading seems a little hit-or-miss as well as I'm staring at the figures and can't really detect their internal lightsource or even intelligent ambient occlusion. The foreground lightbeams could be an interesting render effect if your engine can handle partial alpha in it's layering algorithms, but I feel for a final game, your animated characters need to be both more clearly shaded and a bit less detailed.
Are you just going for a side-scrolling action game like Shadow of the Beast, Altered Beast or Golden Axe on the Genesis? It conveys that sort of feeling also, I'd look into those if you haven't for the amount of detail the figures should really be bearing. Modern games -can- do more than back in the retro era; but it's mostly more work than it's worth. The low resolution of those classic titles is absolutely gorgeous without taking TOO much art-time to be worthwhile.
As a concept. 4/5. If this was in the actual game, 3/5 for the lack of good shading in the figures; though I'd still be stunned to see that detail level animated.