need help in choice b/w games

[thingymuwatsit]

hello all gamers forum users, i need your help in a very big decision and i am relying on all of your input. i am in a dillema because i want to buy both mass effect 2 and halo odst but can only buy 1.
after finding out that odst is relatively a free roam (and i am aware mass effect is too) i am more linear to that side of the argument. But mass effects "bonus features" *wink wink* make me want that too