Kick-Ass is part of its DNA -- the story is adapted from a comic series co-created by Mark Millar, and the two movies share a director, Matthew Vaughn. If only Kingsman had in fact dared to be a bit more odd, it might have really been something great.
There are plenty of hints throughout that the movie was never meant to be taken with a completely serious attitude. Colin Firth is not the first actor you'd think of to play a butt-kicking action hero. Samuel L. Jackson is affecting an odd lisp for no particular reason (save perhaps to enable one joke about the British accent). And the "polished gentleman vs. wrong-side-of-the-tracks" relationship between mentor and student feels like such a cliche that it could hardly read as anything but parody.
Yet for all those clues, the movie plays out with general earnestness for the first three-quarters of its two hour run time. There are familiar plot threads built around that mentor-student relationship, a supervillain and his nefarious schemes, impossible gadgets, and more. Kingsman doesn't feel like it's winking at other movies so much as it's stealing their ingredients for a thoroughly average concoction of its own.
But then comes the last half hour -- a giddy, ridiculously over-the-top display of action and absurdity. For some reason, only then does the movie really let its freak flag fly and make you realize, "Oh! I see what you're doing now!" It turns out Kingsman is as much a send-up of James Bond (and other genres) as Kick-Ass was of the typical comic book superhero. It just doesn't get there until the final act.
Still, there are several actors having fun along the way. Despite what I said earlier about what one expects of Colin Firth, he actually does make a pretty great action hero. Samuel L. Jackson chews the scenery as the movie's villain, in a bit of particularly fun casting now that he's so identifiable by most audiences as Nick Fury. And there are no noticeably weak links among the (mostly unknown) younger members of the cast.
But no matter how deliriously fun the movie gets in the last thirty minutes, it doesn't excuse it not being that way all along. All told, I'd say Kingsman: The Secret Service rates a C. It's an unfortunately missed opportunity.