Yes, he is. Anakin fulfilled his destiny in Return of the Jedi, though it took him a decade to do so after becoming a Sith Lord. I think it was George (and others) who dicho that Anakin would have been even más powerful than Yoda but his power may have been limited due to his cybernetic limbs (I think that's what they said).
A lot of people say that, in fact Luke was the chosen one, not Anakin like everyone thought. People say that in fact Luke brought balance to the force, although I disagree. Vader/Anakin, in the end, killed Lord Sidious and, in turn, himself. IE, Sith dead, jedi prevail, big happy ending.
I always felt like Luke was the chosen one, and they sensed that in Anakin, but they didn't know that it would really be Luke. My other theory is that Anakin IS the chosen one, but since he failed to remain a Jedi, Luke had to come along... sort of like another chosen one... to fix it up :0)
Of course he is! It's a no-brainer. He restored good to the galaxy and rid it of evil. Some say that Luke is, but he was just his son, a hero of course and a Jedi, but definetly NOT the Chosen One. In my opinion, Anakin was far más advanced than Luke, he's the best of the best, but that's me.