AMD is generally very supportive concerning Linux. However, the proprietary fglrx driver drags along a huge pile of crap from ATI that they failed to clean up so far. It would have been best to entirely rewrite the driver from scratch directly after the acquisition, but that wasn't just a huge task needing a lot of manpower, the wanted design just wasn't practicable back then. But now it is about to happen: The fglrx driver will be slimmed down to a simple OpenGL implementation built on top of the core components of the free driver.
	
		
	
	
		
		
			Nearly no games run because the driver does not support required features (Awesomenauts for example).
It would work fine with the official Catalyst driver but then I would have to use old Kernel and Xorg.
Maybe it's better with mobile devices but especially for gaming the OpenSource driver is crap.
		
		
	 
The issue isn't that the driver is bad, it's that hardly any of the companies behind those games cares about the driver - at all. The driver does have a good overall quality and there are quite a lot of native commercial games that run absolutely great with it, e.g. pretty much everything from Valve.
However, it's a world full of dirty hacks and workarounds, anything that is done to work around one issue with a specific driver may backfire with a different setup...