I don't know, driver is experimental so there are some bugs 
But I had make some tests and a lot of things work !
I played to some games like Quake 3 without any bug !
Tuxracer works good to with some bugs somethimes (transparency).
I try mame standard emulation too and it work perfectly !
I play videos in standard mode (opengl output) with vlc, mpv and gnome player.
So you can resize go fullscreen and windowed mode with all this video players !
With the rpi3 even 720p work without any hardware acceleration decoding (not implemented in driver at this time).
With 1080p videos it skips 3.5fps when playing with mpv so maybe with some overcloaking it can be !
Vlc had a bug when you try to go forward or backward in the timeline, but it work good with mpv or gnome player.
WebGl on chromium work good too (with some bugs but it depends on the webgl demo), youtube works better than never and I can read 720p videos smoothly too on my rpi3.
I need to disable media api for that ...
By the way, raspberry pi software using fullscreen old driver output don't work anymore with the opengl driver activate, this is normal and not a bug. The framebuffer output video mode is not enable. So tools like omxplayer cannot work.
I do a lot of tests and the dirver is stable (no crash) but somes icons disapear sometimes or some little display bugs.