We've talked about this before but here's the making of video, they really wanted to make it look like a stop motion film, so a lot of work was done with the way the CG was rendered to make it look that way.
http://www.fxguide.com/fxguidetv/fxguidetv-186-the-lego-movie/
And yes, if you didn't know there is a sequel coming in 2017:
http://www.cartoonbrew.com/feature-film/chris-mckay-will-direct-the-lego-movie-sequel-97296.html
holy crap, I did not realize it was entire CG: http://www.fxguide.com/featured/brick-by-brick-how-animal-logic-crafted-the-lego-movie/. I honestly thought it was stop-motion augmented by CG...
They made it to look that way intentionally as they thought that people would respond better to seeing things in motion that way (which is true really).
Pretty cool I think, what a challenge!