Oh, this looks like fun.
It's tons of fun! In addition to the standard tower defense missions, there are mini-games, puzzles, a survival mode and a Zen garden where you can cultivate the various botanical wonders without fear of zombie invasion. I've gone through the main game once and have completed most of the mini-games, puzzles and survival levels, but my Zen garden is barely getting started. Even after you've completed the Adventure mode (the main game), you can go back through it again with your "friend" Crazy Dave selecting some of your weapons for you (you have a limited number of "slots" into which you can load seeds before each round) to shake things up a bit.