To understand why Disney animation became so legendary, you just need to look at a single still frame from this movie. Pause the action at any point and take in what you see. It looks fine, doesn't it? The expressions look realistic, the composition looks good... Then, unpause it, and you'll understand: Animation is about movement. It's about taking the physics of our real world and recreating them to convey emotion: Excitement, sadness, urgency, rage.
Pixar understands this; it's why they hired so many classical animators. And even their best efforts only match the standard of what Disney and Warner Brothers produced in their prime. Movies like Ark, on the other hand, make another fact painfully clear: Good animators are hard to find, and modelers and programmers are a poor substitute. In fact, there may not even be any animators alive right now who can convey what the artists at Disney did with only a desk, a pencil, and a stack of loose-leaf paper, though some of the people at Studio Ghibli come close.
So any still frame looks fine. But the movement, the changes of expressions, even the inanimate objects - stilted. And with Ark in particular, the problems are worse. The plot is derivative and stagebound, and the pacing is thrown off kilter by tedious exposition, hammering the plot into your ears just in case your eyes didn't pick it up. Frankly, the backstory conveyed in the opening narration sounds more interesting than the film that follows.
Some animation never enters US theaters because of bad luck - take Akira, for example. Then, there are films like Ark - missing them, you miss nothing.
