By far the Halo series. Before all you fanboys who still live in their mother's basements freak out, I don't care how much you flame me, I hate Halo. The story is repetitive and stretched out, the twists are insignificant. I didn't find it that enthralling of a game. Btw, if any of you fanboys bring up the point that Halo 2 was "innovative", let me bring this up, just because you added a twat to a dead pig doesn't make it the greatest invention known to man. Second choice is Assassin's Creed. That game was pretty piss poor, and by piss poor I mean boring. It's too repetitive. That game made me realize that if assassins were obnoxious too-cool-for-school arrogant cliche characters then they really aren't those silent respected killers that I assumed them to be.
Where as the Halo Series scored over a 9.5 each on IGN, I would give it a 3.2, just cause I liked pissing off the Arbiter. Assassin's Creed got a 7.7, which is being way to generous for a game that has you repeat its 15 minutes of gameplay for a couple days.
In contrast I loved the game Chromehounds, so what if mech concepts have been used alot. Chromehounds looked cool and actually gave you the experience of blowing other robots up. The fact that it got a 6.9 (albeit a funny number) is a diservice. IGN... Shame on you.
EDIT: Changed my wording to make it make more sense. I appologise for my poor wording as it's late at night and I need some coffee.