Jarringly identical to his previous Bethesda acting role: Doc Mitchell in New Vegas. (Which broke immersion, forcibly reminding us to think of that character from another video game).
Not to mention his voice didn't really suit the role anyway. His frail, trusting, somewhat-goofy grandfather voice ... didn't actually believably convey the likes of a hardened war general struggling with a passionless goal and buried internal disillusionment.
I would go so far as to deem his performance verging on mechanical.
Anyway, this is pretty much a nitpicking issue. Most of the voice acting and casting in Skyrim is brilliant. And the music is of course f@#king awesome. But this one casting was definitely a fail.
He plays Doc Mitchell? Really?
Weird, I had absolutely no idea, and now that you point it out, I can't even say that it's obvious.
Oh also, welcome to the world of actors. You're telling me that they shouldn't use an actor for more than one role? When you watched Inception, was the entire experience ruined because you just couldn't figure out how he got off that sinking boat and survived another 80 years without aging a day?
When you played the Oblivion opening, were you shouting furiously at your screen for Emporer Septim to watch out for the incoming Klingons?
No.
They are actors, they play several roles. They envelope that role, and we think of them as a character not an actor. Well, most people. And I think he fit the role perfectly. He is a much cleaner, more normal sounding person. He sounds thoughtful and educated, much to reflect the persona of the imperial empire. As opposed to Ulfric, whose epic and thick Czech accent gave the stormcloaks a gruff, down to earth feel.