Plants vs. Zombies. I just beat the adventure mode.
Main website: http://www.plantsvszombies.com/
Minorly useful readme if you get stuck / want to know more about what a particular plant does: http://www.gamezebo.com/games/plants-vs-zombies/tips-tricks/plants-vs-zombies-tips
Japanese soundtrack with the english ending music video: http://www.youtube.com/watch?v=Ofd-SzGweTo
Definitely worth buying.