This was certainly surprising. Like Complich, I expected the movie to be kind of a summary, a (brutally) shortened version of the series, and so when it opened as a totally new story only reusing the characters' faces and names and the basic setting, I was filled with disbelief. It took me around half of the movie to finally accept it fully and begin to enjoy it as its own thing.
That being said, it's understandable the movie never reached the depth of the long series, but it performed almost remarkably well. Quite a few characters were left grossly superficial and acted as little more than plot devices, but once again that's understandable. What was really important: Eureka and Renton's little romance, was jolly good, though. More streamlined than in the series cutting most of the emo away and getting to the point right from the beginning, I'd say.
Definitely worth watching even if it won't replace the series by any means. Though long-haired Eureka could replace the short-haired one any day...