I have no problem running most games under radeonSI. Only ones I have that don't work are Natural Selection 2 and Metro Last Light, which is mostly waiting on GL 3.3 in LLVM 3.5.

For example, DOTA2 / Portal 2 / TF2 all run at ~60 fps with high / ultra settings on my 7870.

There is nothing about driver openness that would impede their ability to run OpenGL games besides the version support, and that is rapidly being remedied.

or laptops apparently