The writing here is the usual brilliant How I Met Your Mother fare. Ted invites Robin to a wedding that she possibly can't come to, because he absentmindedly forgot to check Plus 1 instead of going alone. The whole beginning bit, with Ted staring at the card and flash forwarding near the time of the wedding did a great job of disarming the idea of a disaster like the one Ted created ever happening.
It's just brilliant how it kept on amping up the stakes one after another. Ted, because he has no balls, just doesn't want to break Robin's heart that she can't come after all the work she's done. It keeps getting worse as she even buys some really nice expensive shoes too.
The episode does a brilliant job of making things worse and worse for Ted to the point that he's the single reason why Claudia and Stuwart were going to cancel the wedding. It shows two things, that Ted is gutless, and that he's way too obsessed with Robin.
The gag with the cranberry vodkas was played off really well, loved that part.
What I have to dock points off for this episode is Claudia's acting. Terrible.
Other than that, great episode.