Critics didn't like it because ...
it wasn't PC, back in 2008? See review below, which makes me want to watch it!
Imdb 7.9 and Metascore 67. https://www.metacritic.com/movie/in-bruges
The New Yorker - Anthony Lane
No one wants a movie that tiptoes in step with political correctness, yet the willful opposite can be equally noxious, and, as In Bruges barges and blusters its way through dwarf jokes, child-abuse jokes, jokes about fat black women, and moldy old jokes about Americans, it runs the risk of pleasing itself more than its paying viewers.