Officially, the pale orc Azog was played by giant Spartacus actor Manu Bennett, but there was also a good deal of the character's scenes filmed using CGI and mo-cap. Though that gave the character a more significant size and hellish look, he appeared on screen without the same human essence that came with Andy Serkis' excellent mo-cap performance as Gollum. That has a lot to do with the fact that Manu only mo-capped the character relatively close to release when script changes made him a more substantial character.
That meant that the CGI elves working on the film had considerably less time to render the performance and the character to bring it up to the level of Gollum, and a good deal of Bennett's performance was probably lost in the process. Strictly speaking it is wrong to criticise Bennett's performance here, with the problem coming thanks to the comparatively lack of preparation for the character.
The result was an oddly soulless Azog - the final hangover of a rushed change to the script that promoted him and beefed out his role when Jackson knew he was moving from two to three films. That decision was always going to come with some compromise, and unfortunately for Bennett, it was largely in Azog's rendering.