I played a bit more FIFA 13, going back and forth between my older 720P 42" plasma and the 55ST50 for comparison. Increasing the contrast from 76 to 85 yielded a picture that wasn't as dark and more to my liking, granted it was during the day. I don't have direct sunlight coming into my room, but it still filters through my vertical blinds and around the edges. I played around with increasing the brightness and color a few ticks, but increasing contrast was the most beneficial. I think I will still leave the contrast at 76 until I accumulate some more hours.
I don't know if it's because the 55ST50 is such a big jump in size compared to my 42", but while playing FIFA 13 I noticed a little more jerkiness when the camera pans across the pitch quickly, during long lobbed passes, for example. Also, I could swear that when I quickly pan the camera left and right, when it's positioned in a close up behind the goalie during goal kicks, that I see more blur on the ST50. I keep going back and forth doing A-B comparisons.
I'm going to try Skyrim and Borderlands 2 soon and see how they look. I held off playing Skyrim for so long because I wanted to play it on a larger TV.
I hope that I can get the picture settings dialed in for gaming. So far I'm a little disappointed. When I watched Up on blu-ray via my PS3 the picture was pretty amazing. I can't put my finger on what exactly is wrong with the picture. I really hope that setting tweaks will get me the picture I want and that it is not a limitation of my set.