This episode basically has two things going for it and two things alone. The first is Kevin's response to Robin's question of why he'd even like her when she's such a mess as contrasted with Barney's. The fact that she asks the same question of both her would-be beaus is a little contrived, but it works in this context. Barney's answer that it's because he's messed up too, as compared to Kevin's answer that he thinks she's amazing and hopes someday she sees it too is a good way to dramatize the idea that they offer two very different things for Robin -- Barney offers commiseration in destruction and Kevin offers hope in progress and creation. I remembered disliking Kevin when I watched this show live. Perhaps he seemed like a superfluous third wheel in the usual main character love triangle. But looking back on the show like this, I appreciate how HIMYM makes him more than just an obstacle to Robin and Barney; he's a legitimate alternative to Robin who brings something different to the table, and as he's meshed with the cast more since his first appearance, I've come to welcome his presence rather than resent it.
The other thing this episode has going for it is the ending that ties the A-story and B-story together in the idea that time is relative, and some moments can seem like they last forever and others blow by in an instant. It's a neat theme for the episode as a whole, and time freezing for Barney (contrasted with Ted and Marshall's two-minute pot experience), is an solid visual representation of that.
But those are two scenes in a half-hour episode, and so much of what surrounded them was crap. I frankly love the idea of Ted and Marshall having this pot experience that seems to take hours and in fact takes minutes, but the humor was so lazy and the execution so haphazard that I don't think I laughed once. On rewatch, knowing the trick only makes it seem like more of a misfire.
And I've said before that outside of a couple of good scenes, I've never really found the attraction between Robin and Barney believable or compelling, so the other story centered on them trying to avoid telling their significant others didn't do much for me either. There's some really hacky jokes where they have freduian slips about cheating, and the bit with the singer on the boat singing a song just about them cheating was a bridge too far in terms of the show's magical realism. At least we got some delightfully caddish Sandy Rivers, though!
Overall, this was two good scenes with a bunch of crud to fill in the gaps.