This is interesting because it will mete out all the personal favourites and hopefully some crap I can laugh at. Like
Requiem For A Dream... I can see how it's reputation got to snowballing in the first place and it wasn't CRAP, but it just seemed crass and preachy compared to say..
Trainspotting

A C
ock And Bull Story (2005)
Not critically underrated at all but definitely one of the few great British films of recent times and they are always worth a note these days, being that they're so thin on the ground. Very clever, complex and frequently hilarious comedy. Yes, Steve Coogan actually made a good film that lived up to his television work, and it was this.