Geometry Wars is an excellent game that has kept my interest ever since I downloaded it several weeks ago.
The controls in game are well done. It's dual stick, so you can fire and move in two different directions, which is very original for calculator. I personally use the d-pad for movement and find the XT0N configuration confusing, but different things work for different people. The buttons in High Score entry are a bit confusing, however, since you press Enter to save your score and then 2nd to get back into the main menu.
The graphics just look great. Enemies move fluidly, bullets are clean, and those explosions are just plain awesome.
A fair word of warning: Don't run this on a TI-Nspire in 84 Plus mode! It will crash, and the only way to get your calc back is to reset the 84 Plus archive as well. But it runs like a charm on the normal 84 Plus and the SE.
Verdict: If you have a true 84 Plus or SE, download this game! You will keep it forever.