8.5/10. I kind of hated Ted after this episode when I watched it originally. The way he blatantly cheated on his girlfriend, and lied about it to boot, just chapped my hide. But in retrospect, I feel compelled to go a little easier on him, and I think it makes me like the episode more because of it. For one thing, Future Ted emphasizes that this was a dumb and wrong thing to do, and that he regrets it immensely, and that takes some of the sting away from it. Sure, it's still a stupid, kind of awful thing to do, but having the character acknowledge that in some way, shape, or form, and be legitimately remorseful about it helps.
And, as my wife pointed out when we watched the episode, while Robin has a right to be upset for being lied to, she also invited Ted over with a pretty clear intent (or at least a recklessness) for something to happen between the two of them, knowing full well that Ted was attached. Maybe that should just make me dislike Robin more, but it at least levels the playing field a bit.
And being a little older and (hopefully) wiser than when I first watched the episode, there's something true about it that makes the episode enhanced rather than hurt by the character flaws. People do make stupid decisions that they don't fully think through. Or, in Ted's case, that they do think through (with the conversation with Victoria being a great device to do accomplish that), but act impulsively anyway. The advice from Marshall and Lily underscores the fact that the show gets that, and even if what Ted did was shitty, it's also human, and he has to face the consequences. To work in laughs in that setup and make the awkwardness and poorly considered nature of the whole thing so salient is an accomplishment, and the episode is all the better for it.