I have gamed on the 3010, 5010 and 5020 and can tell you that the lag is not a major concern unless you are a serious gamer (I am). I had no problem pulling running headshots on the 5020 and my cousin games on his 5020 often (we play Borderlands 2 online and he has no issues). Now with that said I can detect the difference from most of my displays that are in the 30ms or less range. So if you are a competitive online gamer with 60 fps games (like COD) then you'll probably want to stay away from the current Epson models. The casual gamer is not likely to be bothered by the input lag however.
I am not defending Epson here either as they should do better being in the position they are in regarding LCD projectors.
I am just giving my honest opinion as a long time gamer based upon actual experience with these units.
Best of luck,