The main flaw is the lack of chemistry been the two main characters, as others have said. This is undeniably true. It's hard to see why they would be friends at all, let alone prospective lovers. But even so, the film is perfectly watchable - and I've sat through many far "better" films which I've enjoyed less.
The individual performances (I could happily watch Reece Witherspoon reading a telephone directory) are perfectly fine, and in a sense the movie is carried by its co-stars: Zoë Chao, Tig Notaro, Steve Zahn, Griffin Matthews. And there's a lot of fun to be had. The film also portrays very clean, orderly, almost antiseptic New York and Los Angeles which border on surreal.
This film is like an after dinner coffee and chocolate; a relaxing, comfortable morsel but hardly main course stuff. I have no problems with easy watchable films, with a bit of humour thrown in. A "great film" it ain't; a pleasant way of whiling away an hour and a half it very much is.
