[SPOILER HEAVY POST INCOMING]
Well, for the most part it acts as the episode 0 for R/B so, that's cool. But it kinda does some cool things with it. We get a conversation between Gai and the Messenger of Light(?) talking about the powers of Rosso and Blu and all. It also shows us some semblance of history of the brothers and Grugeo-Bone. Much like Orb, we get another cool-ass explosion. But, looking at the scene again, it might be bigger than what happened in Orb. In the center, well, we have the stars of R/B. Apparently Grugeo-Bone is OP as heck, he freakin' owned the brothers.
But who cares about all that, if there's one thing the special confirmed, it's that Gai's powers does translate into his Ultra form. Orb can teleport, rejoice! But really, that's some valuable info because I doubt it doesn't mean he can't use it in combat. The writers and directors are just afraid of making him OP.
Another cool thing about the special is that it does an in-universe "passing the torch" moment with Gai at the end, saying "Good luck" to the Minato brothers. Whether that's before or after they got Rosso and Blu's powers, is still unknown however.
On a more serious note, we still don't know what crystals Rosso and Blu have. Did I mention them being defeated by GB had them dissipate into light as well as countless crystals? Yeah, if we know who they have, we can definitely determine at what tier they are at. Actually, hang on. Well, seeing as they have Zero's crystal...
We're definitely having another Low 2-C in our hands. Ultraman is steadily growing in power, that's good.
EDIT: Imma give the short version of what I understand from the previews. R/B is pretty much X and Orb, but the first monster we see is the big bad. Probably.