7.1/10. This one felt a lot like "The Burning Beekeeper" where the gimmick was interesting but the execution left much to be desired. Doing an entire episode in rhyme (with Lin Manuel Miranda!) was a fun idea, but all the show did with it was pitch a pretty standard "three stories" episode, and the stories were barely up to snuff. Plus, the meter of the verses was off in a lot of places and some of the slant rhyme was pretty weak.
Ted's story of whether his outing with a colleague was a date or not was probably the best, if only because it was simple, included one of Barney's trademark "it's a thing" concepts, and had a fun twist at the end with the reveal that the Yankee she'd dated was Barney pretending to be Derek Jeter. Robin's was a bit weaker, with the whole eating the whole wedding cake to regain post-break up self esteem being pretty odd, and the story as a whole not really going anywhere. Still, the worst was Barney's story involving a mafia-esque sitdown with Barney and his various split-screen expys from around the city. It's more cartoonish nonsense with nothing really grounding it, and it wasn't fun or funny enough to get by on that in an episode that was already something of a lark.
Still, the rhyming gimmick gave this one a flavor at least, and I liked the little touches like Ted's story factoring (minorly) in Barneys, or the beat that the fireworks display beside the broken bus is Marvin's first memory. And the return of Marshall's John Henry-esque song at the end was also a treat. But overall this was a fun concept but mostly a missed opportunity.
(Though I will say, I've been mildly impressed at how the show's made Marshall still feel like a significant part of the season even though Jason Segel clearly wasn't around to shoot with the rest of the cast for a good chunk of it.)