Chappie could have been a great film, but instead it is a pretty good one. Its main flaw is giving so much focus on Ninja and Yolandi. Their characters are not interesting and they are bad actors. The story with Patel and Jackman is good, and should have been the focus of the film. Two elements of the film are amazing, however, and are what make it worth watching: the direction and Chappie himself. Blommkamp is a very talented director; his films look stunning. Chappie is very interesting and his CGI looks incredible. All in all, it is a good film, but should have been better.
This movie is much better than many are letting on. If you expect a funny mockumentary mixed with comedic action scenes, and know that Arnold is only in the last act (and is really great in his performance), you will enjoy it. Give it a chance, as it is one of Arnold's more original films.