I really like the ending. Fight me.
Like so much of HIMYM its ultimate message was that life isn't perfect, and things don't always work out the way you planned. It was SO much more refreshing than a candy coated happily every after. And although it was only an hour long, so it felt condensed, in actual fact that final episode covers the rest of Ted's life. Decades. People die, and widowers do tend to find love again in later life.
Honestly I thought it was great.
Sounds like you liked it because it wasn't a happy ending which is fine, but at least accept that it was super badly executed.
They structured a whole season around a storyline about how Ted needed to move on from Robina and how Robin and Barney were meant for each other, but then they trashed it 10 min into the finale.
If they wanted to do this sort of ending right, they needed to do 2 things:
1) Focus more on the grieving of Ted losing the woman of his dreams. Don't turn it into a footnote about how Ted just really wants to hook up with Robin.
2) Make the Robin-Ted-Barney fallout feel more organic. Barney and Robin break up not because of any character reasons, but because Robin's work schedule literally allowed for no time for them to spend together. That isn't a good reason to shatter their marriage, that would wreck ANY relationship. And then they stick Robin with Ted, which is bad because the show spent so much time building up to the idea that they're not meant for each other. Also, frankly, NPH and Cobie Smulders had way more chemistry with each other than Radner and Smulders.
The show did the story equivalent of smoothly driving down a winding road, and then suddenly jerking in one direction off a cliff for no reason. If we aren't provided with a cohesive series of events that led to that car going over the cliff, that isn't a compelling conclusion. A badly done bittersweet ending like the one we got is just a flaming wreckage with no rhyme or reason for how it came about. Maybe it's interesting to look at, but it still sucks.