I'm okay with Ted coming together with Robin and the Mother dying in general, it defenitely makes sense if you look at the series as a whole, but there are some major executionary flaws that can't be denied.
The last season for example, where we spent the whole 22 episodes on one freaking wedding, that was rendered completely void and pointless by the fact that they got a divorce 20 minutes into the finale. It can be excused by the writers being told to write more seasons than they originally planned for and this was the best they came up with, but still.
Then, a lot of Teds narration concerning the mother over the whole series kinda leaves a strange ring to it knowing that she isn't alive anymore when he is telling story. The mother was supposed to be his final "reward", the end of his long path of lonliness and dissapointment, anytime anything bad happens to him he immediately adds that it was worth it as it lead him to meeting the Mother. She was clearly the most important woman in his life, which finally brings me to my last, biggest problem with the finale, the way the Mothers death was handled. Not one minute of mouring, nothing about the surely enormous emotional repurcussions her death must have meant for Ted, generally the complete omission of any grief. Time constraints are no excuse here, as they had more than enough over the last season, and even in the finale itself I can think of a few scenes much less important than that. What's even worse is the reaction of the children after he finishes telling the story with the death of their Mother. No sign of consternation or consolation, just laughing and "Haha you wanna bang aunt Robin". That's just random and incredibly inadequate.
Soooooo this post got a lot longer than I intended it to be, and I just wanna say that I still liked the finale and thought it was a good ending, but a lot of things just don't quite add up.