Niko Bellic is one of the most interesting characters that I've seen in a game, and I dare say that he's stronger and faster than Trevor Philips. Michael Hollick did great on Niko's voice acting even though he isn't really fluent on Serbian.
that thing makes me laugh each time i see it. yes, Niko is Serbian, but AFAIK it's said nowhere that both of his parents where Serbian. it could even have been Serbian by a more far away ancestor. thus, any interpretation concerning his accent can be done