Pretty meh. I'm sure there are some excellent uses of it that I encounter and enjoy without realizing it, but few of the advanced demos work for me (Chrome on Linux w/Intel gfx) or bring my computer to its knees rendering at very low FPS.

It feels like something that was more interested in competing with native than offering a constrained and portable approach.

Quake 3 doesn't work for you? :)

http://media.tojicode.com/q3bsp/

A low resolution static subset of a game from 1999 does seem to work in my browser... I'm not super impressed.