In case you forgot, this article explains how the developers of the latest Thief game decided to not use Garret's usual voice actor because they needed to record the mocap actors' voice. This has become a trend lately as you can also see in the latest Splinter Cell game.
Being able to capture the voice at the same time as the actors' movements and facial expressions, all while the actors play off each other, delivers a much more convincing experience than traditional techniques of recording each characters' dialogue separately and then animating everything by hand afterwards.
Well after playing the game, I can say they should have just scrapped the whole mocap thing or hire a better actor. There is not a single scene where Garret expresses anything. His face is void of emotions. The only acting we see here is awkwardly pausing after another character delivers a line, pacing around the room, to finally reply. It's just so unnatural, and makes you wonder how they thought this was more "convincing".
I overall enjoyed the game but kept being disturbed by the cutscenes. It's really a shame.