Spy is both surprising and hilarious. It's surprising primarily because it was promoted with trailers that did not look hilarious. Instead, they looked like they were cobbled together from old Melissa McCarthy bits. You'd never guess by watching McCarthy fall over on a scooter that Spy is some of her funniest work or that it's fleshed out with her best supporting cast yet.
McCarthy plays a CIA operative named Susan Cooper. She's working in a not-so-glamorous support role as the voice in a REAL agent's ear. She tells Jude Law's Agent Fine when to turn left, where to find the goods, and what's around that corner. She's very good at her job, but she's sick of being so boring. When Fine is taken out of commission, it looks like the bad guys might have learned the identities of the CIA's field agents, so it's up to McCarthy to be the agency's secret weapon.
What follows is funny, but not because McCarthy's character is a bumbling idiot. It's more about her being super unexpectedly good at kicking ass. It's also funny because of everyone else involved. Jason Statham is the movie's secret weapon. The action regular is so good he'll leave you wondering how he hasn't done this sooner. As the turbo-charged Agent Rick Ford, Statham brags about driving a car while on fire and sewing his own arm back on. His riffing is Ferrell-esque, and writer/director Paul Feig gets the most out of him by playing him up so absurdly he makes McCarthy's antics look reasonable.
Spy is the kind of movie that packs in jokes until they're crowding on top of each other, and spreads them around to everyone. McCarthy gets schticky sometimes, but she knows what works for her, and smartly lets players like Rose Byrne and (especially) British comedian Miranda Hart get in on the action. McCarthy works her sweetness to full effect, undermining it with mercilessly filthy dialogue and very explicit and effective physical threats.
Frequent collaborators Feig and McCarthy aren't always perfect. In retrospect The Heat looks like a practice run for Spy, giving the duo a chance to figure out which material to cultivate and which to leave out. The fact that Spy is a total home run bodes well for their next project together, the closely watched all-female Ghostbusters reboot. Let the fans rage at the concept all they like, if it's as good as Spy, it'll be huge.