I liked it, for a beat em up it was really fun. It's a good demo of the bosses/ gameplay but it doesn't really show much more.
It might be good if you showed little snapshots of other sections of the game to try and get people to say 'Hey, there is more then this!'.
The game was put in a small area while most other beat em ups have some form of exploration. The demo makes me feel like there is just a few levels set in box shaped arena's which could get potentially repetitive without some kind of upgrades (Look at some of the games on newgrounds. For paid games, have a look at something like 'Scott Pilgrim', research really helps!)
Oh, I'm also not a fan of the timer. I don't like having a time limit while in a game which seems to be styles at beating up a ton of enemies.
It's all just opinion, I'm no expert myself (Only just barely got into the gaming industry myself as a programmer, working on a project = hard as hell!), I wish you all the luck with your game, criticism aside I did enjoy playing your game ;D