Olga Kurylenko (SPOILERS, maybe)
She is a decent and very beautiful actress, but I wish her character were not in this film. She is its chief problem, in my opinion, and I enjoyed it otherwise. The movie has more than enough main characters to generate humor and pathos between Del Toro, Robbins, Thierry (excellent), Fedja Stukan, and the young Eldar Residovic. It badly stalls every time the Kurylenko and Del Toro characters quarrel. Their you-never-told-me-you-were-in-another-relationship dynamic is far and away the film's least interesting, and the one which feels the most Screenwriting 101 as opposed to the peculiar and well-researched vibe clearly being aimed for.
She is never given anything of substance to do anyway but be a source of frustration for one man and inspire horny, you-need-to-bang-her chauvinism in another.