It’s been a few years since I saw Gunbuster, but certain parts of it are still fresh in my memory. In terms of the grandness of its scale it was certainly rivaled by Diebuster, but I think Gunbuster did a few relatively unique things that set it apart from, and elevated it above, Diebuster. It’s not a secret that I’m not a very big fan of Diebuster, but I’ll abstain from talking about that and instead focus on what I liked about Gunbuster.
First of all, there was the robot training arc in the first episode. Making robots do push-ups and jogging in Rocky-like montages is obviously tongue-in-cheek, but the direction made a very effective character-establishing arc for Noriko, and the fact that it all wrapped up in a single episode was impressive and important considering the series is only 6 episodes long. And the same is true for the (first) time-dilation arc. It did feel a bit out of place to me in the context of the rest of the story, but it pretty quickly established mechanics that become important later on (and even in Diebuster).
That’s not to say that I think Gunbuster rides completely on some of its separate elements, because it’s pretty great in a lot of other ways as well. It looks great, it sounds great and most importantly it’s really entertaining to watch (I’m kind of sad it was only 6 episodes, actually). Now, to be completely fair, Diebuster looks and sounds fantastic as well (though in a different way than Gunbuster), but for some reason it just didn’t resonate with me like Gunbuster did. I guess I’ll leave it at that, but I will say that I do recommend watching both Gunbuster and Diebuster, if only to see two very different-looking shows.