Is it entertaining? Sure is. Is there anything else redeeming about it? Not really. Kingsman: The Secret Service is the sort of movie every self-respecting 14 year old boy should gobble up, and it is exactly as juvenile and undeniably fun as that implies.
You've seen this plot a thousand times before. It's Agent Cody Banks and Stormbreaker, but with excessive blood and some princess booty. It has a few genuinely thrilling scenes, a few gags that are just outrageous enough to be funny, at least one major gag that should have been far more outrageous than it was, and a slight underlying sneer which makes it less gleefully enjoyable than it otherwise might have been.
Collin Firth looks damn classy in a suit, and Taron Egerton does a surprisingly good job of measuring up once the "suit baton" gets passed to him. Most of the action is Wanted-levels of silly fun, only marred by some cheap-looking CG effects. The skydiving scene looks marvelous. Discussions about vintage alcohol are far more engaging than the actual plot. Michael Cain got another paycheck for being Michael Cain. Religious fanatics are the new Communists, fair game for all sorts of cathartic cinematic abuse. Cockney scumbags are still the scummiest of scumbags.
It's worth a look if you're willing to turn your brain off and enjoy the ride. Just don't expect anything particularly intelligent, and don't expect it to carry itself like an adult.