I've always compared the show to Smallville because in both cases, the ending was already known, it was just a matter of how do we get to that ending. And in both cases, the finales left a bad taste in people's mouths because no matter how bad certain seasons or episodes may have been, there was the overall feeling of the ending proving it worth it.
For what it's worth, had the series ended with the Alternate version, it would have been okay. Heck, the mother could have died and they could have left it at that, and it still would have been okay. But for them to kill the mother, and then reveal that Ted is only doing this so he could find a way to tell his kids he's in love with Robin, it completely changes the perception of the show. For me personally, I can't look past any of the episodes where Ted claims to move on, or they both decide that they won't ever work out, it just seems like drama for the sake of drama. Watching the series now, with the lens that Robin and Ted end up together, and the fact that the producers knew this would happen for 8 years, despite how much they tried to say that the Mother was the only one for Ted, it really devalues the journey and makes the characters look bad.