A decent attempt but fell short
This was a pretty good replica of an old school fighting game, straight down to the thin backstory (are you a bad enough dude to rescue the president?) to justify all the beat-em-up action.
Unfortunately, the game failed to maintain my interest to the end. Even though you did a good job of introducing new enemies periodically, the character development system just wasn't robust enough to keep things interesting.
The classes were definitely unique and each had something going for them. I particularly liked the bandit with his two awesome abilities. But the gunner, mage, and robot all operated at such a slower pace than the other two, in a game that's slow to begin with, that I couldn't bare to stick with them. Giving the mage more efficient spells and allowing the gunner to hit multiple enemies at once would help that problem, not sure if anything can be done about the robot since he's slow by nature. Also, some of the abilities were mystifying. I could never figure out why I would want to spend mana into flamethrower for 2 damage per second when i could get far more out of my normal attack, for instance.
Last little nitpicking things I might suggest is that you widen the area on the right hand of the screen where the character has to move to scroll the screen. Could use a little breathing room instead of having enemies appear right next to you, giving you little to no time to react. The other thing would be an invulnerability period after dying. . .it's pretty standard in these kinds of games since it can be a real bitch when you spawn in a bad spot.
So overall there's some good polish on this game and it was fun for a while, but it needs to be a bit snappier to go for the long haul.