I bet, you've already seen everywhere about fans' dissapointment to this series ending. These are "the always-been-told criticsm" points that I agree on :

1. The title "How I Met Your Mother" doesn't match with the ending part. Technically DID, I know, but I just can't see the blue-french-horn from the early episode appears again. So the writer made us Deja vu? So, is it really how Ted met his kids' mother after 9 season? Tracey's presence is just like a little gift after the whole season showed for me. In the end, the point I get is just how Ted was so in love with Robin and asks his kids for permission to get out with Aunt Robin again. 

2. Barney's situation doesn't clear. Who the hell is woman number 31? Are they living together? I know Ellie, the baby who makes Barney's personality change. Salute. But I need to know who is woman number 31. Oh gosh. And then, why must Barney & robin get divorced? I know it's the twist, but I ship them so much. I think, the bad luck you received because the bride appears early is really true. 

3. I need more closure. It was pretty dissapointing when I have fallen in love with "The Mother"s character, but she has to died in the end. What is the illness? Seriously, "The Mother" percentage of this show is really few. 

After pointing out the hate-reasons, so I just realized something about this series from the first one. "How I Met Your Mother" is a series that tells you about friendship, love, and sacrifice, not about how Ted met his soulmate, a.k.a the mother of his kids. This is the only reason why I shouldn't hate the ending. And the fact that the whole 9 seasons always make me laugh, I know if that I want to see something legendary (read : HIMYM FINALE) happen, I must wait for it.