In my mind this is definitely one of the best episodes this show has ever produced. It's funny all the way through, all storylines are good and it's got several very memorable moments.
James van der Beek's guest spot was funny, and the thing with Simon having gone lame and Robin not noticing it felt fresh. And it gave us one of my favorite conversations in the show's run, namely the parent/teen discussion between Robin, Marshall and Lily. That scene could easily have felt boring and like it's been done before, but they made it work through some good acting and by the last line which really made the whole thing work in my eyes. Lily and Michelle were great fun and they managed to save that storyline from "yeah, seen it a dozen times" to feeling original when it turned out Michelle was also suffering from "revertigo" and was well aware of it.
And then of course there's Barney and Robin... I was only a casual viewer until recently, only watching the show if it happened to be on, so I had maybe seen seven or eight episodes over the course of four years. And still I cheered when Barney and Robin got together. Didn't take more than an episode or two to know these two make a really good match. And it was great seeing a softer side of Barney before they hooked up.
Oh, and "Sandcastles in the Sand"... Except for me wondering where the heck you'd make sandcastles if NOT in the sand, I thought it was really funny.