My favourite is Metal Gear Solid 4: Guns of the Patriots though the Batman Arkham games were really great games as well. I also really enjoyed the Mario Galaxy games. It's really hard to choose I'm not sure.
Really hard to say. I think most would consider: Bioshock (ONLY the first one), Arkham Asylum, Mass Effect 2, Dark Souls, Oblivion, Read Dead Redemption, Fallout New Vegas, Modern Warfare 1 (Yes, it was an amazing game) and TF2.
I'd say the Mass Effect series. For all their problems, they still manage to be phenomenal games with amazing replayability.
Mass Effect series is good.
Batman: Arkham City, Far Cry 3, Red Dead Redemption, Bioshock series, Uncharted series perhaps, I'd even put Fallout 3 and Skyrim up there, and maybe the new Tomb Raider reboot. All really solid, enjoyable games.
Playing - FFXIV, Marvel Heroes (UP), SWTOR, Guild Wars 2, Secret World, Injustice, Dragon's Crown, The Last of Us, Payday 2