I was never a huge fan of Gears Of War mind, I don't think I even completed the first one, probably, can't remember though. I hear they're making a third, talk about milking the franchise eh? The same goes with BioShock I guess.
I've just finished playing Lego Harry Potter Years 1-4 the other day, completed it to 100% and gained every achievement. I think it's the first time I've ever done that with a game, but it's definitely testament to how enjoyable the game was. It's currently on eBay now, and if it does relatively well I will have only lost maybe £2-3 in buying it and playing it for a month.
Trading games in is strictly for dumb fucks.
I've been playing the Mafia II demo a bit as well. I really do enjoy it, the simplicity of it. I know the story lasts only around 10 hours, but for me, that's probably a weeks gameplay. I'd maybe only lose around £2-3 again purchasing it, playing it and reselling it so I imagine all will turn out well. I won't buy it for a while yet though if I'm honest, as I've still BioShock 2 I've got to play through, especially since BioShock Infinite looks to be out quite soon. It's just such a creative and artistic franchise, the 50s decor in an underworld utopia is fascinating, but I know nothing will top the first BioShock. If there was one game I could play now having never known the story or played it before, it would probably be the first BioShock to be honest.