"Its staggering to me that he got this part, especially since he seems so completely unbelievable as any sort of 'scientist'"
Well, speaking as a scientist, I can tell you that there are plenty of cocky w*nkers, although I have to admit I don't know how some of them still are scientists.
There are arseholes in every trade.
I'm okay with LMG myself, I don't see anything wrong with his acting (bearing in mind we don't know very much at all about his character or his story arc - from the few moments of the 2 hr film we've seen!)
He is very fit though...