Not bad for a game in it's Alpha-phase. It's playable and I like the soundtrack so far.
Maybe you should include the info's about Herring and Scott's abilities in the character screen ingame + a little funny comment about them (why does Scott look so sad?).
While you continue to make a Beta version of your game, you could not only add enemies (as you mentioned in a comment below) but also some kind of collectable items or gold coins to buy new upgrades (weapons, extra speed, more coins to collect, new characters to unlock and so on). This way you would increase the fun for players and add some replay value to your game.
Hope this might help you. Good luck for the future!