This is something you can't do without, Wii or DS version.
Firstly, what's great about Geometry Wars is the simplicity. I played this game with the Classic Controller and it felt great to simply move with the left stick and shoot with the right, nothing else but the R button which is used for bombing the whole map (limited number of course!). The controls are simple, but the gameplay is where the difficulties lies in.
Though it looks simple, and Asteroid-esk, it's very different. As described before, you are a geometrical shape in space aimed to survive the wave after wave of evil shapes, you shoot them down and gain EXP so your little weapon attachments (things like Turret, Attack, Defend (these are the things that float around your ship and attack an such along with your shooting) and more!) You also gain points in order to buy such weapons and unlock new planets (maps).
Also you are ranked based on your score, fulfill the requirements and either gain, Gold, Silver and Bronze and receive bonus points! Though the game is repetitive throughout, it's addiction level is what makes this game so entertaining. Combined with fast paced and incredible neon lighting graphics, this game is certainly fun and impressive that it makes worth buying.
As a bonus, if you own both DS and Wii versions, sync them up wirelessly, you can unlock bonus maps. Which means more shooting mayhem for the galore!
I highly recommend this game to those who are willing to commit themselves hours of mindless fun shooting. With an addiction level on par with Tetris, I found myself playing it more than I could possibly imagine.