It got old. Fast. The upgrades made it worth it, but the power upgrade pretty much does away with the need for other weapons once you get the first machine gun.
And while I'm on that subject, the first machine gun and the final chaingun are basically the same. All the machine guns have the same firing rate and damage. And yes, I factor in the power upgrade. It would have been nice to get like a lazer beam, or rocket launcher or something. Be creative with the guns, man. Everything was the damn same.
I still have yet to pass wave 47 because of how clusterfucked everything is. That was the problem with wave 40 and on. The area was so cluster fucked I couldn't go anywhere on the screen without getting destroyed. Also kinda wanted to see some bosses at the end of some of the waves. There were a lot of missed opportunities, and the lack of imagination really hurt the overall product.
There were a lot of good things about this game though. The upgrades were nice, and I did enjoy powering up damage and health, then going back to the beginning and raping everything. I also liked how you could reverse powerups. I pretty much upped exp and cash until I got enough to do what I needed then reversed it all and used it elsewhere. I did like that dying was not permanent and making you have to start over. Sure you have to start at the beginning of one of the options for waves, but oh well.
Overall, the game was built well, but lacked imagination which REALLY hurt it. It's not a bad way to kill an afternoon though.