If you enjoy Tower Defense experiences, then I highly recommend this one. It is 100% free on the Oculus Store, and while it is a bit rough around the edges (the menu system isn't a AAA experience), once the action starts it is quite addictive.
For anyone interested, take a look at this gameplay video from @ParadiseDecay
This game has a near perfect rating on the Oculus Store:
Again, this is not a AAA title. It feels Early Access. But it still manages to have a huge addiction factor and is incredibly challenging on Hard difficulty (and above).