It's not exactly his voice, it's the voice acting. He sounds so dull when giving a speech that should be rallying the troops. How am I supposed to believe that we're fighting the good fight when your voice just sounds like "ugh let's get this over with." Also, when you're:
Spoiler reciting your oath upon first joining the legion he sounds really really bored of it, as if he has to be somewhere else or something and the oath doesn't matter at all.
In case you want to hear that specific part to see what I'm talking about, here's a video:
Spoiler
http://www.youtube.com/watch?v=_HqF8HDeRfw
The part where he goes "Long live the emperor. Long live the empire" It sounds like he doesn't even care about the emperor/empire himself, how are you su[pposed to care about them?
It starts about 20:30 into the video, don't watch it if you don't want spoilers.E
Edit: I think his voice fits the character very well if I was to match up a voice with that character's face. However, I think the actual voice acting on important parts of the civil war quest line is just executed poorly. He just doesn't sound convicing at all.