Lost Planet: Extreme Condition.

This demo sold me on the Xbox 360. This campaign is a wild ride, starting with a Halo 2 esque segment with a Kaiju and a small army losing, a time skip, and then following Wayne as he tries to make it with his tiny rag-tag PMC crew fighting monsters you have no business fighting. And somehow the finale is a Mecha fueled shonen fever dream, and every single beat of it is awesome.

And then we get to the multiplayer. This game made me some of the best friends of the late 00s, people who stuck with me for years and years. The competitive modes were serious.