Daaaamn, now
this is how you do a whodunit detective story

It blows MMMystery out of the water so hard in so many ways it really brings home how much better that episode could have (should have) been. In retrospect everything in it was a complete ass-pull, which I guess is in-character for it being a Pinkie episode, but even so all that does is underline how inappropriate Pinkie is as the vehicle by which to deliver this kind of story.
Making this one a Rarity episode means she's playing the detective part not because she's delusional (she straight-up points out that she's
channeling the noir character), but because
attention to detail is both the key to solving a mystery and her own personal strength. It's also the theme for the execution of the episode as a whole, right down to the noir-ified end theme music (Octavia, can you comment on whether this is actually a new arrangement of the FiM end-credits theme, or is it a new piece? I can't hear any similarities, but everyone is talking like it's the same song). The animation details, though, as pointed out above; the careful setup of all the little clues and bits of foreshadowing, like the silk staining and the cologne and the discussion of the record; and shit like this:

He said, and I quote:

Heh heh.

That's the polite yet disingenuous laugh you make when you want to seem happy but really you're not.
Now that is some fuckin' top-drawer self-aware writing right there.
Ultimately the fact that the entire first 8 minutes or so feels like "just some stuff happening in Canterlot" is the episode's biggest strength. You're just watching some backstage dishing between characters, nothing special going on, just another day in pony world. You're seeing scenes like "saying good night in a hotel hallway" and "picking up some broccoli at a reception buffet". And the fact that every bit of that feels so insignificant at the time (and yet so much fun, because it's exactly the kind of slice-of-life stuff that makes the world feel alive and real) is what makes it so much more rewarding later when every single detail they included ends up being key to the resolution of the mystery—and not in a weird, contrived way like the way the pieces fit together in MMMystery, but in a way that feels organic. It really helps, too, that all the clues Rarity uncovered served to implicate Rainbow Dash, so all throughout the investigation you're misdirected into thinking maybe it
isn't the obvious New Friend Geromy who's the bad guy, maybe all this is leading somewhere weird and implausible like suddenly it turns out Lightning Dust or Starlight Glimmer is hiding under the bleachers controlling a robot delivery pony or some shit. When you get the actual reveal, and all the clues start clicking into place, it's more rewarding than you were ready to give it credit for, especially given the way it all plays out considering Wind Rider's status and stature and the awkward fact that he's still standing around there telling them all what he did and how
and yet confident that nobody can or will dare touch him—and then they do anyway! After just enough time goes by that you realize they're not just following the Scooby-Doo script, even if the end result is more or less the same. Ultimately it's all about character and texture and detail, and the structure of the story itself is kind of immaterial and certainly hardly ground-breaking. Which is what has always been the strength of pony.