My all time favorite would have to be the Phantasmagoria 2 LP that was done with a MST3K style commentary. 

To be fair Phantasmagoria 2 is like HALFWAY A MOVIE so it's kind of different than playing some long-ass RPG.  In fact I watched a playthrough of Phantasmagoria 2 at some point just because I couldn't find a download for it and since I was mostly watching it FOR the movie parts then it wasn't much different than playing it.