I thought the mother's character was handled pretty smartly in the last season. Only thing that seemed to work. And now it makes sense why we only saw her in doses. The episode "How your mother met me" turns out to be maybe the best episode of the entire series. The Max storyline pretty much gave full license for Ted to move on after the mother passed.
Spoiler!
I agree, the mother stuff was easily the best part of this season. The problem is, for this ending to work, the audience needs to be more invested in Ted and Robin than they are the mother. You need to leave the audience feeling happy that Ted and Robin finally got togther, not feeling like they got the rug pulled out from under them because this character they really liked is dead.