I've figured out the money glitch.
When I played this a couple of years ago, there was this bullet shaped enemy that would attempt to collide with the tower. Now, whenever it's spawned, your health plummets and money skyrockets; it's destroyed, however, by firing the turret (whether you hit it or not).
Now... for the actual game... offered a good challenge without being too hard. Loved the music choice, but the sound effects got a little annoying after a while.
The circling enemies were rather frustrating to keep up with, and the teleporting enemies were worse - how are you supposed to keep your guns trained on something that instantaneously changes position? The weapons were awesome, especially at later levels - on that note, however, 12 levels was a bit long to wait for the next tier to become available.
In conclusion, 5/5, 8/10. A little disappointing you've stopped updating it; it was a really fun play.