GeoDefense is a fun and extremely challenging tower-defense game, with unique gameplay that combines intense puzzle-solving with arcade action in a frenetic, colorful, vector-graphics environment.
The interface and basic play-style resembles other similar tower-defense games: you drag and drop five types of upgradeable, sellable towers into strategic positions along a preset path to destroy waves of incoming "creeps" (geometric shapes and blobs of varying toughness and speed). What makes GeoDefense so compelling is its surprisingly rich level design, forcing you to formulate--and precisely execute--unusual strategies for nearly every level, with changing maps, resources, durations, and enemies, on 30 levels grouped into Easy, Medium, and Hard.
With such high-quality gameplay, presentation, and replay value, the only potential downside to GeoDefense is that the game is difficult even for tower-defense veterans--so novices may quickly get in over their heads (although thankfully the game has recently added a novice mode). That said, GeoDefense is an absolute must for fans of the genre.