I've been trying out the Rift with a lot of games and love it. Two of the games I've been playing with Tridef are Counter-Strike Source, and Garry's Mod - but not the normal gamemodes. Rather, I've had the most fun playing the games that would seem to least fit the Oculus Rift (but are still first person).
In Garry's Mod, I played two gamemodes - Stop It Slender! and Trouble in Terrorist Town. The former was interesting but not really the best. Trouble in Terrorist Town on the rift is absolutely nerve-wrecking on the rift - people are out to kill you and you don't know who to trust and who is a traitor trying to murder you, and I found that I was scared more by people running at me with knives as I look over my shoulder than I was by the human-controlled Slender in Stop It Slender. So, Trouble in Terrorist Town is one fun game that is crazy to try on the rift
Another game I've found that is absolutely insane (but insanely fun) to play on the Rift is Surf from Counter-Strike Source. For those of you not familiar with the gamemode, it would be easier to show you this video (http://www.youtube.com/watch?v=NChsTIFDYx4
) than try to explain the abstract gamemode.
If you're worried about nausea, surf is the absolute last gamemode you should play. My friend convinced me to try it as a joke and I decided it'd be funny to try it, just once.
And, for some reason that is hard to explain and justify, the nausea makes the gamemode even more fun. The induced nausea feels appropriate as you fly along the abstract ramps - it made me feel like I was actually accelerating and decelerating, which is both painful and crazy fun.
What games do you think would be something absolutely insane to try on the Rift? My stomach needs punishment and I want to try more.