I found this game to be just cracker jack! I really loved every part of it, but the difficulty in later waves can be quite unforgiving. The poison clouds, for instance, make a lot of the first section nearly impossible. Speeding ships during space invaders require supernatural precision. The floor spikes in the running game are a death sentence. I loved it all though.
My only change would be in the running section. Perhaps holding the 'up' arrow could allow someone to hover in such a way that it mimics the other two functions. I do suppose this ratchets down the difficulty though. Forget what I said.
I want to see this bigger and longer with as many new games smashed in as you can fit. Get some crazy storyline going. Also, I loved the 8-bit "Reptillia". Throw in some more of those gems!