The CGI effects and tepid intro will probably bore older viewers, but if you let yourself get into the story, then you're in for a decent time.
My first issue with Jack the Giant Slayer is the beginning. The film starts off with a montage that explains the lore of the giants and then falls steadily downhill after that. I felt like I was watching sequences from a video game as the plot slowly leaks out. The story gets better when the ancillary characters, particularly Ewan McGregor's Elmont and Stanley Tucci's Roderick, become more meaningful. Hoult is fine as the doe-eyed Jack, but he doesn't have any presence to carry the huge action scenes that fill the climax. McGregor does a fine job of being the muscle, resplendent in armor and almost as swashbuckling as his Obi Wan days. Couple his performance with Tucci's vile smugness and we finally have some entertainment going. I'd bet the filmmaker's beefed up the supporting characters during editing to make the film more of an ensemble piece.
The film is effects heavy with wall to wall CGI. Honestly, I was not impressed at first, but changed my tune once the massive action scenes kick in. Darren Lemke's screenplay builds up to a wide array of action, from one on one combat to an all out castle siege. The effects I perceived as too unrealistic at first look much better as the conflicts heat up. I'm not sure if I just got used to what I was seeing, or became more enthralled by the scope of the action. Either way, I ended up liking the film much more because the ending was so well done. Bryan Singer is no stranger to the big pay off ending, so he brings his skill here to resurrect a flailing story halfway through. I saw Jack the Giant Slayer in IMAX 3D, so it's all the more engrossing in the large screen formats.
Jack the Giant Slayer is fairly intense and warrants its PG-13 rating. Numerous characters are killed, eaten, or smashed to a pulp by rampaging giants. In this sense it's not really a movie meant for younger kids. It is a new take on a known fairy tale, but is probably too graphic for small children. The CGI effects and tepid intro will probably bore a few older viewers, but if you let yourself get into the story, then you're in for a decent time. Jack the Giant Slayer is worth the extra dough for the 3D and IMAX, just make sure you hit the bathroom and snack counter in the first hour.