I said this in another thread, so I'll say it here, too: I wasn't sure how to feel about the final moments, but then I thought about it. The entire series has flashed forward and back, and present (the penultimate episode during Ted and Robin's aforementioned conversation up this thread), to Ted going back to Robin. But *she* gave up on him a couple years ago, and chose Barney. He had to go forward, so he met, married, and had kids with a woman he loved dearly. And she died. So...it's perfectly realistic that he'd be able and willing to love again (I agree with Namo, here). They were both available, so... there you go. I don't think it belies the truth of the characters or their personalities, at all. It would have belied them had the finale ended in some fairy tale "happy ending" way.
As for Sutton saying above that it was annoying to have had Robin and Barney's couple-hood be such a focus leading up to the ending, I never quite bought that they'd stay together. Both of them have been consistently depicted as oil-and-water independent thinkers, independent people, who weren't suited for partnerships. The finale shows that with their divorce. It's not a "happy ending," but that's life in modern society.
And yes, as someone else posted above, there have been numerous interviews floating around this week, both with Cobie Smulders and I believe, Miliotti, stating that the show's creators wrote this ending at the beginning. That's why they taped the bits with the kids when they were still young. As an entertainer and broadcaster, I can tell you it is a *major* writing tool that you always know the punchline of a joke, or the conclusion of a vignette or story, when you write the beginning. Comedians do it all the time. It's a skill. And the way they led up to this was brilliant. Life has twists and turns. So, at first, watching and wanting to be entertained, this finale had an initial feeling of "where's the happy ending?!?" But really, it had a realistic, and still lovely one, imho.
Btw, with all the complaints, I haven't seen one person say what they *did* want to see. Yes, it's generally been mentioned that people wanted to see Ted and Tracy together...but what would that have looked like? A close up backing up into a long-shot of them playing around at Christmas in their big house in the suburbs with a bevy full of kids? Ugh. No. Then people would have just said how cliche' it was, and they'd have been right. Just curious.
"There is no use trying," said Alice; "one can't believe impossible things." "I dare say you haven't had the practice," said the Queen. "When I was your age, I always did it for half an hour a day. Why, sometimes I've believed as many as six impossible things before breakfast." --Alice in Wonderland