I think ultra-realistic/immersive VR games could be quite dangerous if they were so immersive your brain couldn't differenteriate between the game world & reality.
Have you heard of the phenomeomen where people who fall from a great height actually die before they hit the ground? Apparently they die due to the stress/shock of their impeding doom, or maybe it's a natural defence against the horrible, albeit momentary, pain of impact.
What if a VR game was so immersive it tricked your brain into believing impeding doom was imminent & it just shut off?
Also what about phobias in an immersive game world? It would be terrible if you were arachnophobic & playing a VR RPG, then suddenly you opened a treasure chest & were swarmed with spiders. Also I think vertigo, claustrophobia, agorophobia & pyrophobia could be real dangers in a immersive VR game, especially if you weren't aware you were a sufferer until it left you a shaking, piss soaked mess on the floor of your local VR arcade. There's probably a phobia for every aspect featured in video games.
Or what if you're character was hypnotised in a VR game? I know TV programmes aren't allowed to broadcast actual hypnosis because it can affect the viewers, I'm sure it would be even more of a danger in a immersive VR game, especially a MMORPG which could potentially be hacked by malicious Cyber-Hypnotists.
All in all, I think VR has lots of issues to address & safeguards to be implemented before it will be available for the mass market.