Matt as the Doctor
i'm pretty sure every one thought he was going to be horrible as the doctor. But that's only because he was soo young, and he was completely different to David Tenant. And people don't want to let go.
People only wanted actors similar to Tenant, which misses the point of Doctor Who. He didn't try to copy David Tenant's personality as the doctor, He came up with his own unique character, which makes him a very talented actor, because it worked. There's no chance it would've worked with Matt if he tried to follow Tenant as close as possible. The casting people obviously saw something new when they saw Matt Smith. He manages to keep the vital characteristics that most of the doctors have, and at the same time be completely original.
And in fairness, Matt Smith must've been very brave, to have enough confidence to show the audience a new doctor. Because no one wanted a new doctor after Tenant.