I use a GSM Galaxy Nexus, stock, no overclock, no frills, just rooted to use Titanium Backup, never had any lags in Fruit Ninja, runs fine... Temple Run, ocasionally will stutter, but it is rare and most of the time I just play 20, 30 times and no stutter at all... GTA III also plays fine.
Obviously it is not the best performer, and, as you probably now, there is the same iPhone 4 GPU under the hood of our devices, only that it got extra memory bandwidth and extra clock to perform better (and also a HD screen that will eat-up some of this extra performance)... But I believe, at least as far as my own experience goes, that it is a decent performer, altough there are better alternatives as far as gaming goes (and I would believe that probably HTC One X would be the best Android gaming phone alternative as far as graphic performance is concerned right now).