Must have is subjective, but aside from your list, I like:
Onward (Kinda srsbsns)
Pavlov (Less srsbsns)
War Dust (64 player Battlefield. Bloody loving this right now!)
Zero Caliber (Bloody downloading this right now
)
Google Earth. Not a game, but awesome nonetheless.
Star Trek: Bridge Crew (Best with mates, and helps if you're at least a little bit of a trekkie)
Gun Club VR (Single player doing a load of active target range stuff. Better than it sounds)
*Insert racing game of choice*
Lone Echo (Don't have low ceilings or anything breakable near you!)
Skyrim (if you're prepared to mod and fancy playing as an archer/mage)
Arizona Sunshine
Conversions: Alien Isolation and Doom 3 BFG.
Dunno what your motion sickness tolerance is like, so a lot of these might be a bit iffy if you haven't got the legs yet