Make the intro cutscene skippable. People want to get into gameplay right off the bat with these kinds of games, so forcing players to sit through a couple minutes' worth of exposition before pressing a single button isn't a wise choice.
Apart from that, I really liked what you have so far. The way you melded pretty much every single gameplay mechanic into one weapon is pretty genius; a lesser developer would have made the platform gun and the "shoot zombies" gun two separate things.
Good work.