I've had very long sessions in the past but struggling to really feel immersed by any game recently, had a few longish sessions (2 hrs) on Crysis 2 but didn't feel fully immersed.
The Half Lifes, Deus Ex, Dragon Age, Oblivion and others seemed to speed up time, you'd sit down to play and the next thing you know several hours have passed, not sure if it's todays games or me but I can't seem to get into that mode nowadays.