I should preface this by saying that I'm not much of a sitcom fan, in general. But for the past few years, How I Met Your Mother (by Carter Bays and Craig Thomas) has been my exception to this rule; I began watching because of Alyson Hannigan of Buffy and was sufficiently charmed and entertained by the whole ensemble to keep watching. The show is now in its fifth season, and while it's had its ups and downs, it has remained reasonably solid, although last night's episode didn't really rise above "mildly amusing." Still - and this is the one place where I think sitcoms have the advantage over hourlong shows - keeping up only demands about twenty minutes per week, so I can tolerate "mildly amusing" if it involves actors I like and guest stars like Will Shortz and Arianna Huffington.
What is becoming intolerable, however, is the show's framing device and, by extension, the title it inspired. For those who haven't seen it: the show nominally takes the form of a guy named Ted telling his teenaged kids the story of - yes, you guessed it - how he met their mother. It makes for a memorable title, sure, and it was a decent hook for the first few seasons, but after five seasons it has been stretched beyond its capacity to carry the show. (Thankfully, Neil Patrick Harris could carry practically anything.) A more general version of the device would have worked better: Ted telling his kids about his life before they were born would have made for a premise less gimmicky and more enduring.
By calling the show How I Met Your Mother, though, Bays and Thomas have written themselves into a corner. For the first few seasons, there was speculation among fans and critics as to how long the audience would put up with not meeting the mother. I haven't seen that discussed much recently, presumably because everyone has given up caring. Framing device aside, this is really an ensemble show, and I don't hear many people calling Ted their favorite character. The majority of the interesting plotlines have centered on the interactions between this ensemble, not on Ted's search for a wife.
The title also suggests that the show might end once Ted meets the mother. I don't think that's even worth worrying about, because the real problem is that the mythical "meeting the mother" event demands either an entire lack of suspense in the plot or a complete betrayal in the narrative. Ted has met and dated a variety of women throughout the course of the show, and, presumably, the audience - and the children to whom Ted is telling this story - are supposed to wonder whether each woman could be the mother. But this doesn't actually make any sense. These are teenagers. Absent some sort of crazy THEY'VE-never-met-their-mother plot twist, they know their mother's name. They know what she looks like, and what kind of work she does, and at least some generalities about her background. So the instant the mother appears, either the kids will say "Oh, that's mom!" or Ted will become a fully unreliable narrator. (He's always been somewhat unreliable - glossing over drinking or sex while talking to his kids, for example - but it's generally done with a broad wink at the audience.) And I suppose a third option is that Ted won't lie about the mother, but that the audience will be asked to believe that the kids are oblivious enough to not pick up on it.
There's really no good solution here. Given those three options, I guess I'm hoping for the first. They should do a quick reveal of the mother - maybe during the season six premiere - and then let the characters, and the show, just move on already. Trying to actually change the title of the show once the mother appears probably wouldn't work for marketing and branding reasons, but I think if the show acknowledged that the mother had been met and the title was irrelevant, the audience would just let the title issue go and keep watching. HIMYM deals with issues of young people figuring out how to pursue adult goals without losing themselves or the friendships that mean a lot to them, and there's certainly enough there for the show to continue without the increasingly-boring "mother" drama.
(One last note: Bays and Thomas have a new show coming out in the fall, and it's called the pleasantly meaningless Livin' on a Prayer. I hope this means that they've learned their lesson.)