The film suffers because it doesn't appear to be that sure whose story it is actually telling; is it the zoo-keeper's or the panda's? It should be the zoo-keeper's; a story of unrequited love that just happens to involve a talking panda, but the lure of such a charmingly disenchanted panda is too great, and the two stories get in each other's way as each weakly battles for top spot but fails to dominate the other.
The film looks good, the panda looks great, and there are some genuine nice moments, but ultimately this is a great idea let down by lazy writing and poor dialogue. The impression given is that the filmmakers were so wrapped up in the mechanics and visuals of bringing the panda and his world to life, that they overlooked the simple fact that the heartbeat of the film lay with the human characters, specifically the zoo-keeper and the object of his love, and freezing them out with uninspiring exchanges and very poor dialogue has the effect of leaving us out in the cold with them.
As is the case with so many of these kinds of films, the problems were undoubtedly born at script level, with character and dialogue overlooked in the heady excitement of the film-making process. You can't help wonder what the outcome would have been had the filmmakers not been in such a rush to show the world their comedy panda, and took some time out to engage in a proper character/dialogue rework and polish.
It is a real shame, as I believe this had the potential to become a true cinematic gem.