I feel for you taking some hard reviews, especially after putting in so much work and for so long...
I think that your art style is quite unique (that's not a good or bad thing) but it doesn't seem to fit any genre of comics I recognize (I don't read that many comics, so I am totally prepared to be wrong about this). My point being that, with such a non-mainstream style of character drawings, you are not automatically appealing to a majority of potential players who are looking for eye-candy. When you're looking to market anything, you have to strike a balance between selling your soul to appeal to the mainstream and satisfying your inner-artist.
My advice would be to think carefully about the style of the characters (what you have is not to my taste, to be honest, but you don't need follow my advice here). You could maybe make it work in the current style if you had some real killer animations. Lots and lots of smooth eye-pleasing animations would bring people begging to get some of your game (as long as the game-play is challenging as well... if it's 1/2 fun to play with just substitute blocks then you're on the right track; if it's boring as hell then you're betting too much, perhaps, just on how it looks).
How you go about that is up to you - my advice would be to investigate Spriter because it's integration into c2 is awesome (if you don't just export the spritesheets) - it's really easy to create smooth animations and animation transitions. Which is what your game doesn't have today. Also, I know others have mentioned this as well, the characters take up a lot of space on screen - that's ok for a comic, where the characters don't move, but it's not so good for a combat video game...
I don't think it's as simple as just swapping out some pixel art and then it'll be "job-done". Also, as I have learned, you need to get feedback from people who are prepared to be openly honest with you, so you can address any gameplay concerns before you go to market. Perhaps too late in offering this advice, but find some people who aren't concerned about hurting your feelings and get them to play through what you've done.