What I like about Breen is that he isn't portrayed as some super charismatic Andrew Ryan or the usual Far Cry villain. He's intelligent, sure, but he's also just a boring dry academic that got picked to act as Big Brother. I'm pretty sure he knows exactly how much of a powerless middle manager he really is and all his ramblings about immortality, evolution, space and the awesome science humanity will get to do is largely just cope on his part. He's also the only reason humans didn't get immediately exterminated and knows how easily the Combine could wipe them out if they felt keeping them around wasn't worth it anymore.