I'd say two. Galaxy & Metro. Guild Wars 2 is when friends want to party up.

I don't play more than one story based game at a time.

I still have to wrap Rayman: Legends up (I´m not sure if I will go for 100% though)
I am on the last case of Ace Attorney 1 aaaand still have to finish Mario&Luigi: Dream Team Bros.
...an Kingdom Hearts: *insert wacky name here* arrived today
...too many games, not enough time D:

I am about to start Professor Layton 3, I'm preparing for the finale which will start in November :(
I'm also replaying Apollo Justice for AA5 and I started Hitman 2 two weeks ago.

I´m so giddy knowing that I still have 4 Ace Attorneys to play before going to AA5 ! (The series is absolutely incredible !)

Investigations isn't needed to be played. It's has no ties from what I've heard.

I will still play it before :D (when I can find a copy for a reasonable price....the AA games are insanely expensive in Germany)

...I will still buy AA5 on launch day to support the series in the West !