You've got something interesting here! I think with some work on controls and spawning I could see this game really clicking with people. Maybe zoom out the camera a bit, too.
The weapon changing mechanic is fun, though I wish I had some control over when it changes. Also it would be great if each weapon had particular advantages and disadvantages. It's fun to have a specific reason to be using each weapon. There's a great turn-based game that uses a similar weapon-changing mechanic, called Morphblade. It's super good and pretty cheap to buy, and I'd recommend you check out what that game does. Good luck!