I have to go with Knights of the Old Republic 2 (including patch fixes). The characters and storyline just really immerse me into the game. Hopefully one day we'll get more good games and maybe even films of the era.
All time favourite game....I'd have to be honest and pick Halo 3. First Xbox I have was 360, raced through the first 2 games in time for its release and it floored me, I hadn't witnessed anything as cool as it before and I still go back and play through them. Yes Crash Bandicoot, God of War, Gears of War, Dark Souls and all were amazing and I love them as much, but I can consistently play through and enjoy Halo 3 every time. The story was amazing.
Elder scrolls V: Skyrim: One of my first PC games and the one that I’ve put in tons of time and replays. Watching it change of time with tons of mods. It really peaked my interest in RPGs and set the bar very high for me.
The whole franchise is my absolute favorite gaming series, the second game best of the three. I got really sucked into the Mass Effect universe, lore, characters, everything. Read all the books, still waiting for the movie...