There have been a lot of reviews of Death at a Funeral. Here are a few which comment on Matthew Macfadyen's performance:

The mostly Brit ensemble is a delight, notably Macfadyen, whose likeable, long-suffering everyman provides a solid center for the swirling s--t storm

The cast is first-rate, especially Tudyk, Donovan and Andy Nyman as a hypochondriac who gets something awful in his mouth.

Boasting a tightly knit ensemble, unlike the erratic casts in such earlier Oz efforts as "The Stepford Wives" and the uneven "In & Out," the movie's standouts include Tudyk, Andy Nyman as a weasel-like hypochondriac and Macfadyen, the comic embodiment of glum.

Of particular note is Matthew MacFadyen as the nominal lead, eldest brother Daniel, whose long-suffering normality in a storm of dysfunction makes him the perfect straight man. Another favorite is Andy Nyman as the schlubby hypochondriac Howard. One of several not-quite-lovable losers, his humiliations push the lowbrow comedy to new heights.

The cast, too, has plenty of gifted actors, especially Rupert Graves and Matthew Macfadyen (Mr. Darcy from Pride and Prejudice, only here a tad pudgier) as the two main figures, feuding brothers who are incapable of setting their differences.