He was, I thought, quite dreary in Torchwood: Children Of Earth, but then I remembered he played Caecilius in DW: The Fires Of Pompeii and was actually quite fun. He might be OK.
I think they had to get away from casting relative unknowns because the character is getting very deep and needs a player with a bit of gravitas. The only other actor who has come to the role already very well known was Peter Davison and although he wasn't my fave, he was certainly a lot better than a few I could mention.
Still, the main thing is, Matt Smith is GONE and that can only be a good thing.