7.5/10. This is one of those episodes that nails the ending so well that you kind of forget what came before. The reveal that Lily is pregnant with Marshall and Lily's second child is done pretty wonderfully. It provides a great resolution to Marshall/Lily conflict, specifically one about competing dreams, with the great beat that Lily is and has already given Marshall his dream -- to have a family. Their embrace and decision to go Italy, (which is admittedly a little too perfect with Mickey and Judy there) is beautiful, and the twist that their daughter's name is Daisy, after the flower where Ted found the pregnancy test (it's sweeter than it sounds on paper) is a nice capper.
The problem is that the lead up to is so-so. I like the idea of Ted thinking he's uncovered the mystery of where Lily went, why she got into the car sent by the Captain, and so forth. And his theory that she's been smoking is a well-thought-out red herring. But the episode really drags it out, and while they lampshade it a bit (with Marshall's line that "this is going to be unbearable") and some meta-stuff toying with the act break structure, it still drags before we get to the emotional catharsis.
The B-story, about Robin's mom telling her all about how bad Robin's dad was to reassure that Barney is nothing like him, was pretty weak, mostly because the suspicious similarities between the two don't cohere with anything we've seen or heard about Robin's dad. The upshot is that it feels like a forced bit of conflict and attempt to sew doubt about things, even if it's played for laughs and Barney gives her a big hug at the end. There's lots of great ways to show Robin having concerns about Barney (and lots of great reasons for her to be concerned), but twisting things into an "oh god I'm marrying my dad" mode just doesn't scan.
Overall, a mediocre episode with a powerhouse ending.