The rainbow crystal arc really, really, really, really grates on me. As I've said repeatedly before, I like filler! Filler is the heart and soul of Sailor Moon. But there is such a thing as too much filler.
This is what the rainbow crystal arc is to me. It's eight weeks worth of too much filler. Even if all eight episodes were good it would be too much. See, the problem is that they start a padding arc well over halfway into the show, where essentially nothing much has happened except for the awakening of four Senshis. I can understand why they did it, as the manga needs to catch up with the show before the big final arcs. (It never really does catch up, though, hence the Doom Tree arc).
But, ignoring the real world constraints, the rainbow crystal arc feels completely unnecessary to me. There's literally no reason we couldn't've done this across Jadeite and Nephrite's arcs - which are now essentially pointless in retrospect - instead of punting it across the halfway episodes. Each Senshi gets a focus episode here but that's nothing that couldn't've been done at the START of the show instead of the other filler episodes.
If there was eight solidly good episodes in this run, maybe it would be more acceptable - but that's not the case; a few of them are instead really mediocre and quite boring to watch through. Make getting the first four rainbow crystals spread out across the previous arcs to make them actually having lasting impact, and then put four episodes into padding here instead. That way you can keep the extra padding to let the manga catch up but without the slog of having to sit through this arc for two months!
As for the episode itself; it's mediocre and skippable. The only thing of note is that Rei's shrine gets a new apprentice, her grandfather is a monster, and Rei acts like a total bitch the entire way through. The apprentice has a much better role a few years later in an S episode, so I might as well mention him now. The episode gets a 1.5/5.