Read Dead Redemption is still by far the most beautiful game I have ever played. Sure, there are other titles that might looks sharper, brighter, crispier - but what RDR delivers is the mood, the depth and the sense of the real environment surrounding you.
Recently I cam across this site called Eurogamer and they have an amazing time lapse video that shows off exactly what I'm talking about. It shows a few day/night cycles from different locations. Dust clouds twist across the desert. Sun rises and sets. Beautiful. Apparently if you just leave the controller alone the game starts showing off its vistas. Who knew!?
I got about 70% done with the game and sort of put it on back burner without finishing - this just made me want to dust it off get get back on it. Watch the video here.