Not bad for a first try...
...So don't get discouraged by my low score. I rate a game based on how well it holds up to other Flash games, not on how good of a first game it is. So! Here's some honest feedback on what was good, and what to change.
I actually really liked the visuals. It was easy to see what was an enemy and identify where you were because of the color contrast, and everything was detailed enough to make it appealing. I don't know if these are your sprites or you got them from another source, but if they're yours, kudos to you!
Now, here are a couple of problems. First of all, there's no overall quest, story, or even motivation for what we're doing. There's not even a real punishment for losing; I just jump back in and start all over again. This would be nice if it was a fast-paced or difficult game, but because there's no real context for what we're doing, it makes the experience very bland and uninteresting.
Second, there's a complete lack of a difficulty curve, upgrades, or really even different enemies or enemy placement. All enemies just swarm you from the beginning, and you're dropped in the middle of it all without instructions or a reason for being there. Some sort of tutorial, accompanied by a steady rise in difficulty, could vastly improve this game.
Overall, it seemed like more of an experiment to me, a beginner's project. While there's a fair number of things that could be changed, there's also a lot of potential for growth. I hope to see you progress and evolve as a game designer.