It was a great stand alone, but it's largely inconsequential for the series. Joel and Ellie don't end up interacting with Frank/Bill. Most of the episode doesn't really move the story forward, and only exists to give more context to characters that are no longer part of the show.
In a weird way:
- it's amazing by itself.
- arguably bad as part of a series.
- probably really good for people who played the game, and wanted more background on how Joel and Bill knew each other.