First of all, Jack getting a movie has been a running joke ever since Fables gave it a reason (no spoilers, read it!). I have been ticked to death by the fact that someone in Hollywood actually went there.
Second of all: the entire thing benefited helluva lot from using great actors. I speak for quite a few people when I say that I would listen to Ewan McGregor and Ian McShane read the phone book, and Nicholas Hoult has been steadily gaining momentum as a very talented young actor with cheekbones to die for. Anyhow.
From this point on, my opinions have greatly been colored by the fact that I am a professional storyteller who has spent two years studying in Appalachia. Which more or less means that I could probably tell you Jack's shoe size with three source references if you woke me up at 3am the morning after St. Patrick's Day. Yeah.
I have heard people complain that the Jack movie is not realistic and ridiculously over-the-top.
People, meet the fairy tale genre. Fairy tale genre, meet people.
I have to admit that the historical reenactor in me had mini-fits all through the movie when weapons, costumes and armors were considered, but in the end, it just gave up the fight and accepted it as part of the generalistic nature of fairy tales. One exception was Jack's costume, which had nothing Medieval about it whatsoever, instead he was pretty much wearing jeans and a hoodie. I could totally get behing that. Jack is an eternal hero, every generation needs their own.
Hollywood is still not getting the whole "independent female hero" thing quite yet, but they get an E for effort. The princess was the weakest link in the cast, but at least she was a link. Keep workin' on it guys, you'll get there eventually.
As for the story itself: I appreciated the small things. The best wink to the folktales came from a line the captain says to Jack "You killed one giant, and that makes you an expert now?" And yes it did. The giant-killing was well done on Jack's part, more smart than strong.
The ending of the story was a great plus. It gave a very neat run-down of how stories change from generation to generation, which is kind of the point of the whole thing (also, a fun twist in the tale). There is no "original" in folktales. If someone wants to take Jack and the giants and play with them, they can do so. Some people will like it, some people won't. That has always been the case. I am not even saying that it made my top list of favorite movies, even though it was fun for a Saturday evening.
But now there is not only Snow White and werewolves and Avengers on the daily menu. There is also a guy called Jack. And he'll be sticking around for a very long time.