It helps to bear in mind this movie's real purpose — fan service for the infamous niche character's evident legions of followers.

Rating: 8/10 (6 March 2016)

I've never read a single "Deadpool" comic book, but that didn't stop me from enjoying the movie. It's a fun, creative and  unconventional entry into the "X-Men" film franchise that actually made me laugh out loud a few times. I'd give it an 8 out of 10.
It isn't high art. It's got a thin story based on a rickety plot device, nearly no exposition, and it includes some cartoonish action that I thought was just too over the top, even by comic book movie standards. (Our hero dodges bullets and survives a stab to the brain.)
It helps to bear in mind this movie's real purpose — fan service for the infamous niche character's evident legions of followers. "Deadpool" isn't meant to be densely plotted, like "X2: X-Men United" (2003), or genuinely cinematic, like the Christopher Nolan "Batman" films. It's a long awaited, R-rated feature film to please loyal fans of this profane, adult-oriented antihero, who would be out of place and necessarily bowlderized in a mainstream superhero- teamup flick. (And I kinda get that — I loved the "Wolverine" comics when I was a kid, and, trust me, his film incarnation is tame compared to its source material.)
"Deadpool" is damn funny. The movie succeeds by making us laugh. And combining a raunchy comedy with an "X-Men" film gives it a weird, cool, subversive vibe. It makes you wonder if Stan Lee would approve of this sort of thing  until you see Lee himself in a cameo at the story's strip bar. It's fun to know that dirty jokes indeed do exist within the "X-Men" movie universe.
The lowbrow jokes made me cringe one or twice ("baby hand.") But you've got to give the movie credit for delivering its bathroom-wall humor if that's what the original character is about. (Are the comics like this?) Ryan Reynolds is genuinely funny, and his deadpan delivery is perfect. The film might not have even worked at all with out him.
By the way, this movie actually reminded me a hell of a lot of a long-ago flick that I absolutely loved, but which I'm guessing is largely forgotten — Andrew Dice Clay's "The Adventures of Ford Fairlane" (1990). That movie also had a foulmouthed, lone, maverick antihero who often broke the fourth wall, and that also made me laugh like hell. I know it sounds like a strange comparison, but they're very similar films.
Finally, I'd like to think that the Wade Wilson we see here actually IS a version of the Wade Wilson that we first met in the widely lamented "X-Men Origins: Wolverine" (2009). (And how can he not be, if that movie is canon?) If "X-Men: Days of Future Past" (2014) rebooted the timeline, then the Deadpool we're rooting for here was never recruited, corrupted and experimented upon by William Stryker. So you can have your cake and eat it, too.