So, since Fallout 3 won't work on my computer, Steam issued me a $19.99 store credit. However I have no idea what game to get. I usually buy games based on people's recommendations or if I've played it before at a friends place, but recently I haven't been getting out much, and I don't want to end up making a random choice and wasting the store credit on something lame.
I love open world type games where you can just wander around and not worry about the main quest, without getting bored.
I've already got (hardly any I know):
Fallout: New Vegas
S.T.A.L.K.E.R SoC and CoP
TES: Oblivion.
Age of Empires 3.
Rollercoaster Tycoon.
Hoarding stuff is also a bonus, I enjoy games where I can steal my enemy's shoes

If anyone can just recommend me to some good games that have many hours of gameplay and is close to what I've mentioned (but preferably a different series, i.e not Morrowind or Fallout 1), that would be much appreciated.