One thing the tutorial missed--training doesn't end itself. I got like 5 levels ups and 291 points of dodge by the time I realized I could end my marathon myself.
This game is really hard, but I'd rather have a really hard game than a really easy game, because it'll last longer and if you can ever finish it it feels like quite the accomplishment. After playing this in 2009, I still don't have the hard badge...
*Gasp* The poison towers are programmed not to re-poison, but to poison everything before firing the same target twice! You've made me the happiest TD player on Earth!