I liked it, actually. I believe it's a pretty good ending, and it all makes sense.
SPOILERS:
The story is centered about Ted's relationship with Robin and the mum only comes in the last part of the series.
In fact I always thought that the mum would have been a random actress, but that wouldn't have been a surprise. I mean, "ok, the mum is going to be a random actress, what's all the hype about?"
The fact that Barney has a daughter from a one night stand is perfectly fitting with his character. If you act like that you have to be aware of consequences. I loved Barney from the first episode, and I believe this ending is perfect.







