I do think this was a great animated short. PIXAR really outdid themselves with the hyper-realistic CGI in here, and the simple story of a blue umbrella falling for a red umbrella in a sea of indifferent, monochromatic umbrellas. The subtle expressions of their surrounding environment can really captivate future animators who're looking for something to build off of.
Unfortunately, it's slightly awkward to watch in a theater, as it comes before Monsters University, and it makes me feel as though some people may have walked into the wrong movie. I really want them to enjoy it, but because of its placement, it's hard to do so.
I'm sure PIXAR had good intentions placing it before Monsters University started, but with a bunch of kids coming in to watch MU, I don't think it will garner much positive attention. I, for one, like it, but parents of rambunctious kids may not find it funny when their kid starts to act out from boredom. Maybe those kids will appreciate this short in the future, but not today.