Played this on my iPod like crazy in High School, but finally beat all the maps on PSP tonight. It's far too punishing to be enjoyable, but is packed with charming design. You'll be playing a LOT of it if you choose to puzzle it all out yourself like I did, but it's a must for tower-defense die-hards.

Otherwise you can definitely pick a better title to play, but you should still stare at it, longingly thinking about what it could have been, for a while...