I have definitely seen better sci-fi, but it is still enjoyable, even if only for the looks.
The story is your typical good versus bad uprising spiced with a bit of love here and there. It is nothing original and not even the best execution of such plot. It would really benefit from more "gray" in its strictly defined black & white characters (and no, one is not enough). But this may be just my longing for the worlds like Witcher by Sapkowski, which is the very best example of moral grayness.
If there is anything Wonderful Days has to offer, it is the graphical aspect. I am not saying it is a pure awesomeness from the beginning to the end like Karas, but it has some pretty impressive scenes. If you can get an hd version, don't hesitate. Even now I am not sure if those drops of water in one scene were real or not ^^.
The soundtrack does a decent job of supporting the visuals, but it is nothing I would listen to days after seeing the movie.
If you want some sci-fi eye candy, grab an hd version of Wonderful Days, but don't expect too much of it.