Two weeks ago, 'Home Wreckers' felt very much like a step in the right direction. Ted was finally putting the first pieces into play in terms of his long term goal. While he didn't know that it would be the home he raised a family in, for us as an audience, it finally felt like the writers were saying, 'Okay, let's get on with it already.'
This week, however, with 'Twin Beds', was very much a step back (for Ted, and arguably Barney). It's not usually a problem when the characters are living in the moment, and the plot doesn't rely on a storytelling device that assumes a foreseen conclusion. Take, for example, 'The Big Bang Theory' - if Leonard and Penny fall out, it doesn't feel like a step back because that's just the story as it's being told. Barney and Ted thinking they're still in love with Robin was a one time (I hope) story that was an otherwise well done take on the 'I want her because I can't have her'(*) sitcom storyline; here though, it just didn't fit. We know Robin won't end up with Ted, so there are no stakes in the matter.
(*)Arguably the best interpretation of that was in 'Scrubs', where JD finally had Elliot and then immediately realised he didn't want her now he had her, and chaos ensued.
Marshall and Lily's twin bed subplot was a nice little thing on it's own that had plenty of merits - Marshall's d-bagness is a version of the character that Jason Segel plays really well, and him rejecting Lily after sex and making her do what must be the world's shortest walk of shame back to her own bed was very funny.
Ultimately though, the episode relied on Barney and Ted's drunken(**) quest for Robin to carry the beds subplot, and it couldn't. Some good jokes here and there (particularly Barney eating all the hot food to try and intimidate Don) but not the most memorable episode.
(**) Josh Radnor also isn't the best at playing drunk, and next to Neil Patrick Harris, who is great at pretty much anything, he looks a bit weak.