actor/actress's preformance can be easily recoganized and judged from small films. However, big project like OB is doing right now, with excellent cast, actors' preformance is usually ignored in turns of big scene.
We can see from previous Academy Award that Best actor and Best actress often produced from those low cost flicks. Like this year, "Lost in Transition", "Monster", "Mystic River"... bluh, bluh, bluh..... which are not that popular comparing with LOTR, are likely to win some important awards, such as best actor, actress, and supporting roles.....
So... I think it is not because OB can not act well, it is because of the type of film he is playing, and the actors/actresses he is playing with.
But... some people like to complain. So rediculas!