Sitcoms should be a place where you can escape the realities of first world problems. Now HIMYM is serving it up like cold leftovers of the harsh reality that is real life. I don't want that much reality thanks!
In The Wonder Years final ep, we learn that Kevin and Winnie end up just being friends after an infatuation that goes on for, like, forever. (sounds like Ted!) Kevin's father dies (like Marshall!) The whole show was narrated by an older version of the main character (like HIMYM!) The last ep was depressing - because it was boring real life stuff.
Most shows get cancelled before they can wrap things up and we are only just now in the era of shows designed with an end in mind.
How I Met Your Mother is past its expiration date. They've drug things out for the sake of dragging things out, and I've personally grown completely disinterested with where they're taking things. At this stage of the game, I legitimately couldn't care less who the mother is going to turn out to be.
It doesn't help that the cast have only stuck around due to contractual obligations because the apathy has carried over to the performances. Jason Segal has even gone on record saying that he'd rather be off doing other things, and I think it shows on screen. Aside from the arc that dealt with the death of his father, you can tell he's just no longer invested in Marshall; I can't really say that I blame him, either. The jokes are stale, the story-lines forced and uninteresting, and, well, the magic's just not quite there anymore. None of this is to say that the show is bad, per say, but it should be pretty obvious to anyone actually being objective that it is a shell of its former self. Big Bang Theory is getting dangerously close to heading down the same path (if they haven't veered that way already).
To HIMYM's credit, at least it hasn't turned into The Office yet. That used to be my favorite comedy on television, and now the hair on my arms actually stands up from the embarrassment; it's excruciating to see what's become of it. If the science in Eternal Sunshine were actually a thing, I'd happily have the last 4 seasons completely wiped from my memory. Just, so...ugh. :(