8.3/10. First things first, I am still amazed at how well they introduce The Mother. There was such potential for disaster in writing a character who needs to be perfect for Ted but also feel like a real and distinct person. Grand kudos are owed to the writers' room and Miloti for what they pulled off. Pairing her up with Lily was an ingenious move, both to show how The Mother would fit in with the group with how quickly the two of them bond (albeit a little conveniently) and to show how she and Ted are well-matched via Lily's complaints about him (the "Mrs. Tedwina Slowsby" gag had me in stitches). Miloti and Hannigan have a great rapport and it pays dividends for The Mother's first outing as an actual character.
Barney and Robin thinking they might be related was mostly fluff, but it was entertaining fluff! I like the continuity of Barney rooting for the bad guy (his comment about King Joffrey of GoT having parents who were related and nevertheless growing up to become a "fair and just ruler" was a big laugh) and the reveal that their shared cousin Mitch was adopted after his biological parents were eaten by wolves, and the couple's ensuing relief, was a nice dark gag resolution to the whole ordeal.
In a storyline that was pure fluff, Marshall also attempts to tell his mom how to delete a facebook photo over the phone, so as not to reveal to Lily that he accepted a position as a judge. Most of the humor was pretty mild, with "old people don't know how to use technology" and "baby miraculously solves problems" leading to cute but pretty unadventurous jokes. That said, there were some mild stakes to the storyline which kept things humming, and Lily not wanting to look at the picture despite the alert because of Judy's "emotional blackmail" was a nice touch.
I'm less enamored with Ted as the real "wild card" at the wedding. I forgot how late in the game HIMYM introduces the whole locket thing, and I've already said my piece on the love triangle angle of the whole thing. Still, I like the meta-sweetness of Ted giving Robin a picture of the gang when they first started hanging out (hey! that's the picture from the show's title screen!) which works in-universe as a fakeout for the locket and out-of-universe as a nod to this being the show's final season.
Overall, a nice way to kick of the last year of episodes of the show and set a number of the season's major storylines in motion.