The Series messed itself up in a big way as it got closer to the end. You lost its sense of direction and the character building was not working towards a resolution, but rather unwinding itself. the Series tried to be a slice of life, but then ended up trying to be something else. This hurt the series in a big way for me.
the movie on the other hand .. . .
this movie heavily outshined the series. The aspects of the series which fit into the movie were amplified, but the things that the series screwed up were amplified by the movie too.
Story: The feels that occured in my mind during this movie built up and built up. By the end you are in such a good mood with the characters. They also integrated the the roles between the alien and the time traveler extremely well in this movie, which added to the plot. By the end you will feel satisfied that there was meaning for what happened in this movie.
Animation: A little bit better than the series, but not extrodinary.
Sound: nothing immensly awesome, but as the "feels" increased it seems like the quality and music did too.
Characters: they did it right in the movie. The series messed it up. the movie fixed it (mostly). And at the end you are satisfied with how the important characters developed. Really good job in this movie.
overall: definitely worth a watch, you should probably see the series first (if you have the patients), but I think its worth seeing it so that this makes more sense.