I technically have this rated a tick or so higher than the full series, though that's less due to any particular strength displayed by by this, and more to the disappointing ineptitude of the series. I probably wouldn't have even bothered watching it if I knew it wasn't officially a part of the first series (it's added on digital platforms—itunes, anyway—as a 13th episode). Which probably describes why most people (now, anyway) watch this: They don't realize the series ended with episode 12. (Pro-tip: If your viewers don't know the series is over, you've probably fumbled the narrative.)
(MAL's review system demands I add more words here, but this isn't worth more words. Is this enough? Let's find out...)