The game is enjoyable for the first time but it's not really fun to play it a second time.
I have to agree with you about the theme, as we really disliked it, too. The snowman theme was a much much better candidate as a theme (IMHO).
A few more notes:
- the screen is simply a frame around the game and is IMHO a bit too small.
- put the screen more "front-facing" to the user: reduce the angle at which it's viewed.
- the top snowman drawing goes beyond the screen(!!)
- snowballs disappear a little too early, without reaching the end of the screen.
- to win it you can just stay in the central position and press fast the up key.
- this kind of games (shooting battles with another enemy) are very difficult to balance out. They are usually either too easy or too hard for the player, so try to avoid them :).
Sorry if I'm a bit too harsh with my comment. This wants to be constructive so you can improve on the next LD.
I may guess wrong, but I had the impression that you probably spent a lot of time on the background image and found yourself rushing for the game. For the next time start with a planning phase on paper. Decide what your game does and how much time you need for each feature. Delay the graphics at the end, after the game is done! :).
I also suggest you to do LD with a friend. It's much funnier than being alone :)