First time playing Oblivion and I saved after like 16 hours at the end of the session.
Mass Effect, Mass Effect 2 and Mass Effect 3 have probably all been 15-20 hours in a single session. I'm pretty sure I did my Hardcore and Insanity runs in Mass Effect one the same day one after another. Skipped all non-essential missions and hammered through it. ME3, I had been playing all day when I got to the Cerberus Base that is the point of no return. The last two missions took me hours and it was after 6am when I finished the main game. I was so excited to see how it ended that I didn't want to stop - if I had known how long the missions were and how slow I'd be on my Insanity run I'd have left it off another day. Going to work for 9am the next day I felt like a zombie.