There isn't much competition in this category, admittedly, but MacGruber is the funniest Saturday Night Live-based film since Wayne's World. We'd have breathed a sigh of relief if it were merely not awful. The fact that it's actually pretty good, a gleefully silly action parody that doesn't run out of steam before it's over, is just icing on the cake.
The recurring SNL sketch it's based on is a spoof of the 1980s TV series MacGyver, famous for its resourceful, duct-tape-wielding protagonist. MacGruber, played by Will Forte, is ostensibly just like MacGyver, with the joke being that he's actually dangerously inept. (Each sketch ends with him and his crew being blown up.) The movie version, written by Forte and SNL writers John Solomon and Jorma Taccone (Taccone also directed), expands MacGruber's character to include several more traits: cowardly, petty, vain, homophobic, delusional, immature, and maybe sociopathic. Like many characters played by another SNL-bred Will -- that'd be Mr. Ferrell -- what's so funny about MacGruber is that, despite being the hero, he's an awful person who's terrible at his job. I mean, people die because of him. Regularly.
Forte and company have logically put MacGruber into an '80s action-movie scenario. A former Navy SEAL, Army Ranger, and Green Beret, MacGruber is retired now, Rambo-style, when his old Pentagon friend, Gen. Faith (Powers Boothe), recruits him for an important mission. It seems a nuclear warhead has been stolen and must be found before it is deployed. And who is the thief? None other than the same dastardly villain responsible for the death of MacGruber's wife. The bad guy, played by Val Kilmer, is named Dieter Von Cunth, primarily so the movie can make its characters say "cunth" over and over again.