I think Viggo Mortensen is one of the most underestimated (and underworked) actors in Hollywood, although this might be partially his choice too, since I know he's an accomplished painter, photographer, musician, and poet, among other talents, which means that maybe he just never meant for his acting career to take over his whole life.
I also consider him one of the most attractive actors out there, and in Eastern Promises both his masculinity and his craft are in full display. This is the movie in which, famously, he has a fight scene in a sauna during which he's wearing no clothing whatsoever. And he delivers.
The movie is quite violent and graphic, so it's not for the faint of heart, but it's a good story, with a couple twists and a lot of tension, and the whole cast is very good, although it's Viggo who shines above all (he also got an Oscar nomination for it, so finally someone did notice him).
A good thriller.