First of all: congratulations for your first entry!
The sound and music is actually quite good. Also the gun model has a perfect complexity for a Ludum Dare game.
Here's some feedback on the game:
* The controls feel very unprecise, as if walking on ice. Also gravity should be stronger.
* The game is missing some actual game mechanics. Why should I shoot the cubes if I do not get penalized (e.g. loss of health, some push, loss of energy for the gun, loss of vision, ...).
* Frankly spoken, shooting some cubes is rather dull. If you add some motivation, e.g. you are a rockstar who is in bad need of a toilet but has to chase away groupies before your bladder explodes, the whole game gets more fun.
Some general hints:
* You can also edit the text of your entry. No need to write a comment yourself with more explanations ;D.
* For a Ludum Dare a FPS is maybe a bit ambitious if you just get started. Restricting oneself to a 2D game is a very good training and also one has to fight with much less complexity.
* If you want to get comments, you should definitely play and rate other games. This will give you better visibility and therefore more comments.
* Make sure you make another game at the next Ludum Dare!