I loved that Cillian Murphy used his real accent (and his apparently unpronouncable name - a woman reviewing Intermission on Radio 4 pronounced it 'Sillian', which was amusing). Also, he is hot. I never really noticed his hotness before. Perhaps it was all the running around in the nud which he does in this film.
Also, Christopher Ecclestone was great, as ever. He's very good at playing charismatic loons. Some of the best television ever was the three parter in Cracker where Robert Carlyle played the lefty-turned-psycho-skinhead and Christopher Eccleston was the police inspector he killed, which gave both of them a chance to do their best "I'm mad/ruthless" acting. Top stuff!