He's essentially playing the same character with the same exact mannerisms from Always Sunny, but just as a doctor/scientist. Frankly, not much range.
I saw the movie last weekend and it was okay. It's not going to win any awards. The story line is a bit weak, but the fights are mostly entertaining. I mean, come on, giant robots fighting alien monsters? It has the cliche love story as well. I found the music score to be irritatingly overdone. About 60 minutes in it became distracting to me. Still not a bad way to spend a boring afternoon.
Perhaps someone could explain why the robots waste the first 60 minutes of the movie trying to pummel the kaiju to death with their metal fists instead of using their swords or ranged weaponry? That seemed very odd to me.