I love the way you use particle effects, the ice one looks especially cool! (...pun not intended, I swear)
Without the enemies telegraphing that they're going to attack, the only strategy I could come up with was to circle them, wait for them to fire, and then go in for the kill. Also the camera being so far zoomed in meant that I was sometimes getting killed by enemies off screen.
As for the theme, having only one player in a wave based game like this isn't particularly novel, pretty much all of them are like that. The design challenge for this GameJam is less about picking a style of game where you only have one of something, but picking something that normally has lots of something and making it only one.
Great job on getting something submitted in 48 hours, be sure to do it again sometime and make something even better! : )
- Joe
(if you get the time to check out our game, we'd really appreciate it!)