I would like to suggest 2 things:
1) A way to sort shop items by price
2) Auto-combat against creature attacking you. Especially when they're behind something and I can't click on them directly.
A couple of suggestions: 1) An indicator on when a wave is due to finish. 2) Bombs kill enemies as well as players.
Also, without an infinite chainsaw, how do you avoid a wave of zombie dogs?!?
I too think it's a good game but I got bored after a while. Maybe if it was broken up into stages? I hope as the game progesses there are more enemies types (not just strengths or sizes) and powerups.
I SO want to rate this game 5 out of 5 but the Bloodthirsty and Millionaire awards are too unreachable - even with full strength. I finished every level at least 4 times each and I'm only at $30,000.