This app was mentioned in 4 comments, with an average of 2.00 upvotes
I was about to come and post the same thing!
Also, I'm a fan of InMind VR: https://play.google.com/store/apps/details?id=com.nivalvr.inmind&hl=en
The successor, InCell VR, made me a little too nauseated.
Deep Space Battle VR is pretty cool too: https://play.google.com/store/apps/details?id=com.gamearx.spacerumble&hl=en
These all have some variant of "look to fire/do action" mechanism.
One of the first games I downloaded for Google Cardboard was like that - you shoot viruses (virii?).