This movie is heavily criticized by the Saint Seiya fandom, however to be fair is a very competent work. The story happens after the Hades arc, and it shows very well the consequences of these events: the gold saints were punished and turned into a statue, Seiya now is in a wheelchair, in a semi-vegetative condition. This was a smart decision, because it shows that conflicts have consequences, what was not done in other sagas of the franchise, in which the protagonists simply win without side effects or losses. Also, the saints do not have the same faith and confidence in their powers, what is veryrealistic, since the golden saints are absent and Seiya has not the same power from before. All this contributes to create a much more real scenario, in which you really feel that maybe the protagonists will loose in the end. Other factor that makes this have sense is that Athena apparently abandoned Earth, which is now in the control of Artemis.
In terms of animation the movie is very good: the colors that were choosed combine perfectly with the idea of a Sky saga, the action is fluid and dynamic, and more importantly: the art is capable of expressing the emotions and feelings that the story needs.
In regards to the theme it is coherent with Saint Seiya as a franchise: the mortals challenging the gods, what is very well developed, with Seiya regaining his power until he can face the gods and angels. The end is a controversial one, but I personally love it: it has impact, it is strong, and it expresses the thematic that was developed not only in the entire movie, but also in the original series. In conclusion, Overture offers a version more realistic, thematically coherent and well animated than the majority of the series, being in my opinion the highest point of the Saint Seiya franchise.