good concept, but ultimately boring
Some complaints:
1. Despite a decent number of items and upgrades, the number of combinations worth considering is very small. For example, the healing components didn't seem to be worth it in any of the battles, and trading for better weapons with weaker armor always seemed like a losing decision. I noticed that shots don't travel through obstacles. This is interesting, but you might take more advantage of it by offering a weapon that shoots over obstacles.
2. The AI was really really simple, and the behaviors looked quite dumb, but I know it's hard to write intelligent looking AI. It could also be the case that you spent a lot of time scripting certain kinds of smart behaviors, and I just didn't notice them because they were too subtle. Of course these are problems that the entire game industry is facing right now. You may consider giving the user options for combining different kinds of AI, for example, stick together/spread apart, focus/distribute fire, engage/retreat, and choosing which targets to attack first before the battle begins. This would make the game a lot more interesting, and also give the user more of a sense of control over what's going on.
3. Each level is not that different from any other. There didn't seem to be strategies that worked in some and not in others.