If you don't have plans to see this movie, you can check the spoilers here and then come back.
From far away, Epic is pretty, but once you get up close, you notice the cracks; this can double both as an assessment of the animation and of the movie overall. The widescreen aspects of work done by Blue Sky Studios' animators is gorgeous, as they create a well thought-out, meticulously constructed, inventive world that shimmers and shines from the outside. The action scenes, particularly the chase sequences, are packed with frenetic energy and the animation really nails the details. It's when the characters are standing still or conversing, when the action slows, that you notice the little things like facial expressions and figure movement don't hold up as well. Similarly, the grand premise of a hidden nature world where there's an ongoing war between the denizens of life and the avatars of "the rot"--seriously, it's Rotworld!--is cool, but it feels at times like the folks writing the script figured that skeleton was enough to hang the plot on and didn't really need to flesh their mythology out. The second half of the film is a lot stronger than the first, which really drags, but by then it's coasting on the forward momentum provided by action in lieu of a strong story or character development. The voice acting is of varying levels, as Amanda Seyfried and Josh Hutcherson are fine if a little flat in the leads, Colin Farrell puts an effort in as the aging hero of the piece, Christoph Waltz gets about half way there as the villain, and the trio of Aziz Ansari, Chris O'Dowd and Steven Tyler get to stand out because they're the comic relief and this is a PG-animated movie (the less said about Beyonce's performance as the queen of the forest, the better). I wouldn't trash Epic, as it's a perfectly fun piece with some really strong craftsmanship times, but in an era when animated films have hit a much higher level, it feels incomplete.