Last major purchase for the steam winter sale...What should it be?

[Book Smarts]

I want buy one more thing from the Steam Winter Sale(I already bought like 6 things, and I'm almost broke ), but I'm wondering what games are worth the money.

I'm split between...
Arma II Combined Operations (Day Z)
Mass Effect Collection
Fallout 3 & Ultimate Edition Fallout: New Vegas
Bioshock I & II
Assassins Creed I & II
Serious Sam 3

Any recommendations from this list of games?

[Little Judas]

I know Fallout 3 is worth it's money and NV is always fun. (3 is better in my opinion)
Bioshock is something my cousin speaks very highly about.

[Animalia]

Mass Effect and Fallout 3/NV are both really good, haven't played any of the others so I can't say how they are but I do know those two and would recommend them.

[Chishio Kunrin]

Assassin's Creed is a pretty great series, even though the first game is a bit glitchy at times. My favorite in the series so far is II, so there's that.

[Book Smarts]

Assassin's Creed is a pretty great series, even though the first game is a bit glitchy at times. My favorite in the series so far is II, so there's that.

Yeeeeah, I've seen some good ones, but I'm willing to give it a second chance