Karl Urban did McCoy wonderfully. He was by far the closest of the bunch. Simon Pegg is good in anything he is in, although I don't think he got Mr. Scott down. But the poor bastard is isolated on a cold barren place, with no liquor, MRE's (which still taste like dogcrap in the 23rd Century) and a muppet for a companion that he loathed.
(I'll expand later)
Yes, I agree with you on McCoy I think Karl nailed him. I was very pleased he got it right since I was a fan of Karl since his Xena/Herc days. I was really worried if he could pull it off... he was amazing.
And for Scotty... you know he was the one character who bothered me. I don't know why, I didn't like the snipes at the little alien, just seemed too much for Scotty, I don't remember he being overtly nasty.
And James Doohan is Scotty to me, so I guess that was just too hard to let go of. But then again, I loved Zach as Spock and Chris as Kirk so... I don't know, maybe Scotty will be more likeable next time. Could have been the script.