This is by far the best tower defense game i've ever seen. it has a perfect dose of stragedy and difficulty and offers new devices for killing those creeps. this original concept of dens, crypts and temples- as oppose to arrow tower, cannon tower, flamethrower- is a great idea. this game is also a pioneer for the levels and skills system, which really adds to the gameplay value and also increases replayability; as in order to get those brilliant ranks, you need to upgrade your special abilities and tower effects. i eagerly await 'don't touch my gems! 2' which could supply even more great concepts and even more creep blasting levels of fun =D
i agree with Tsushi, you get points for drifting, points add on, the highest scorer wins. not rocket science (although rocket cars would be pretty sick =b )
 "Cursed Treasure: Don't Touch My Gems!"){kind=icon}
 "Fantastic Contraption Prius Edition"){kind=icon}
 "King of Drift"){kind=icon}
 "Bubble Tanks 2"){kind=icon}