Which games are "essential"?

Ok, so I finally got a 360 a few days ago. These are the games I have: Assassin's Creed, Gears Of War 2, Grand Theft Auto IV.

I'm getting two more games in a couple of hours, but there are A LOT of games that I want, So I don't know which ones to get first. Here are the ones that most interest me:

-Bioshock

-Fallout 3

-Dead Rising

-Soul Calibur IV

-Mortal Kombat vs DC

-Mass Effect

-Devil May Cry 4

Which ones should I get? HEEEELP