I was a bit surprised when I replaced my Radeon HD5870 with a GTX 580. Surprised at the difference in image quality. I went from a GTX 7900 ( I think ) --> Radeon 9800 --> 4870 --> 4870x2 --> 5870 and then a GTX 580.
I switched to a GTX 580 due to the "lack" of general performance increase in the 6000 series and also due to the debate about image quality.
So when I first fired up the GTX 580 to play some COD Black ops I was really surprised at what I saw. I didn't expect any major difference going in but boy was I surprised. The image is just so much sharper and the colors so much fuller. Maybe there is a better technical explanation, but I'm just describing what I see on he screen. Thinking that it could just be COD Black ops I tried another game ... Left 4 Dead 2. I play L4D2 a lot and since it's not a TWIMTBP title (and steam complains about my Graphics adapter being unknown) I didn't expect much difference to show. But boy was I wrong AGAIN !!! The same thing goes ... much much sharper picture, more vibrant colors etc. and I'm talking about a game I have logged hundreds and hundreds of hours in playing on high end Radeon Hardware. No matter what game I try it's the same story, much better image quality and more vibrant colors. You could argue that it's just a matter of adjusting settings in the control panel and it could be, but since I just got the GTX 580 I haven't changed any settings in the control panel and it's at default settings.
I'm a bit surprised about this and also a bit disappointed, because since the GTX 7xxx days and the GeForce FX + 3DMark 2003 days ATI has always been a guarantee for image quality for me. I hope that AMD/ATI will find their way onto the right path again and not play these games of cat and mouse where they do AF correctly in AF tester (when it's detected) but differently in games etc.. Picture quality is more important to me than FPS and I hope AMD will realize that too. So what if they loose 10% performance by rendering things the right way, it's a lot better than the bad press they get on this.