I'd have to say Bioshock, followed by Batman: Arkham Asylum.
I think with both games though it was the fact that I had owned them for so long without really getting in to them. When I finally sat down for a prolonged play I realised what I had been missing out on.
But they really do have that 'pageturner' effect you're talking about. The games are self-contained within one giant area, but effectively broken up into levels. And the more I played both, upgrading my character and having the story progress, the more I would think 'I'll just do this one section and I'm done for the night'. Then repeat the same thought 5 or 6 times. I'm usually pretty bad for completing games, but I'm sure both of these rank as my top 2 quickest completed games. I even started Batman on the hardest difficulty the day I completed it on normal.