It is important for a number of reasons, which means that most discussions about anime as a medium will reference it on one point or another. The quality of the artwork and animation is objectively superior to most of its contemporaries. It also succeeds independently as a film, and not just an adaptation of a manga, despite a rather (in my opinion) drawn-out climax. It’s not surprising that you found it “overrated.” Given how important it is to the genre, it’s hard not to have it built up to the point where it can’t help but disappoint when you finally get around to watching it. But whether you like it or not, the people who make the anime that you do like very probably draw at least some of their inspiration from the manga and film.