I have tried the game on Intel HD3000, and the game runs smoothly. The problem is some flickering and missing light (its always like dawn, with no sun) except in the virtual mirrors (full light as it should be).
The first time I tried changing graphics, as you said, mouse lost the focus. I closed the game, changed the graphics, and no losing focus this time.
Screenshots also weren't working because of the light problem (2 od 10 came out good, others just rgb colors).
Will try on Ati and Nvidia later.
I've tried the game on an intel hd 3000 on both mesa 8.0.4 and mesa 9.1.1 and in both cases the game runs as in it starts I can hear the sounds but it shows only a black screen, I don't currently have any other video cards where I can try it on so for now this is a showstopper for me.
What are the plans to fix mesa support?