If I had to rank my top 5 I would say; TES: Morrowind, S.T.A.L.K.E.R. Call of Pripyat, Mass effect 2, Mount and Blade: War Band, and the Witcher 2
The top two simply because of the modding communities that support them (Morrowind overhaul 3.0, Misery for COP) I’ve put so many hours into both games and just get lost in the immersion.
The whole Mass Effect Series is just great story telling and interesting characters, I know most people didn’t like the ending of the 3rd one, but I found it appropriate for the series.
Mount and Blade is probably the reason why this game caught my attention, of course it looks like crap and isn’t incredibly intuitive, but man its fun slowly taking over another kingdom.
And if any of you have played the witcher series, I don’t need to really explain, highly looking forward to the third one!