Wow - I must be playing a different game than all these whiners. I've only had one level that killed me a few times, and then I just used different towers and I was fine. The gameplay isn't great, but if the game is difficult for you, farming isn't necessary - just try something different. You know - use your brain!
Excellent graphics but the gameplay needs some serious balancing - and then it's still tedious. I assumed after a few waves, it would move on to something different. It's just the same thing over and over - quite boring.
Fixed now, don't be so angry:).