My 3 year old loved it. I loved it, my wife loved it. So 10 out of 10 from our family. As for violence level? Not really that violent, mostly of the slap stick variety. Nobody truly dies, no gore, no blood, no torture, so it certainly is appropriate for children, much more so than many Saturday morning cartoons.
This movie really takes the idea of CG movies where it should go.
First of all beautiful graphics, textures wonderfully done, with true depth, not trying to be realistic, but forming an artistic whole. The moss on the stones, the rust on metal, the reliefs on the wood and the stone, everything adds to the whole.
Character modeling, unlike many contemporary CG movies, is quirky, not cute, again within an artistic whole. The faces may look less malleable than in some other movies, but the characters are more puppet-like than human-like. I think that is a good thing, it lends veracity, how strangely it may sound, it is easier to suspend your disbelief.
Hair, fur, clothing, on par, at least with the likes of Pixar. Just note in the opening scenes when Lian-Chu is fighting the giant slug; Gwizdo is in front of some farmers, and all of them have detailed clothing which caused me to pause the movie just to admire it.
The setting. Far beyond the likes of Cars, and even WallE. Space has been done many times, but the fantasy environs of Dragon Hunters are only comparable with some scenes in Never Ending Story and Lord of the Rings, but again it is an artistic whole, and with lots of good ideas thrown about effortlessly. Magnificent vistas like the scene in Monsters Inc. where they ride all the doorways through its storage facility, or WallE where we see the immense trash towers he made, abound in this movie, everything is grand, yet never dwelt upon; it is just the background the whole way! The interlude where they walk through the area with the fantastic falls. The Chinese wall, the islands floating in the sky. The Broccoli in the sky? That is truly where I believe CG should go, make something which takes your breath away, and do it again and again.
The sound is good, the music is varied and not only epic, and thankfully without any vocals, and purely original for the movie.
Animation is quite good. Lending its inspiration to cartoons, especially some good use of stretch and squeeze. Sometimes not that realistic, but the 3d models are not realistic either.
Characterization is well done too. Lian-Chu the gentle and uncertain giant is gradually growing in confidence basking in the attention of little Zoé.
Gwizdo the wily manager of Lian-Chu redeems himself in the end, while Zoé isn't really changed at all, but who wants that cute child to change anyway? I at least loved Lian-Chu more than any other recent character since Sulley in Monsters Inc.
The internal strife in the group gets ironed out by the external pressures, just as it should in a proper fantasy story.
The story is mostly reminiscent of the Never Ending Story, especially how the world brakes apart. The monsters are pretty standard fare, except the flocking one. It lacks the emotional impact of WallE, which is the really strong point of that movie, but it is a much more fun ride, and lacks the annoying musical scene replaying in the former one, and has action from the first scene. This movie is what you want to watch for a fun and exciting time.
The whole movie has, as I've mentioned a whole vision, which seems to have been followed rigorously throughout.
It seems, that the setting is ready for more adventures, and I for one would hope so.
One side note, the French actor doing Lian-Chu sounded a bit like Jean Reno at first, but I'm happy it wasn't him, though he is one of my favorites. Nice to hear a new, to me, voice.
I give it a max rating, a bit surprised at the mediocre and low ratings by some; I have tried to address some of the concerns made by two of the reviews with the lowest vote. Approach this movie as an adventure, and as a European movie, not opposed to Hollywood, but different.

"Whipped" is one of the most awful films of all time. It is a mean, hateful piece of garbage that had me forcing myself to stay in the theater more than any other movie of 2000, besides maybe "The Grinch." It is not, as people have called it, an insightful portrait of modern relationships. That would be a little film called "High Fidelity." Whereas that movie was honest and sympathetic, "Whipped" is hostile, cynical, misanthropic cinematic poison. Avoid this like so many plagues, unless you want to see how truly bad a "comedy" can get.