Informative review. This can really just be looked at as an extension of the main series. There is really nothing here that is special in its own way—it's really just the typical plots—enough so that it differentiates from the main series. What you find in the original is also present here, just new stories are to be found. The only main difference that really exists is the new character designs; the eyes changed. The character change doesn't harm experience and although it is noticeable enough to get your attention more times than not, it is nothing drastic or experience-ruining; it is something to take note of asyou go on in the series. The OST lies in a similar situation as the original in terms of quality and variety. It just has a different OP and ED.

I would go ahead and watch this if you liked the main series, there is really nothing to lose here truthfully. It's not like this is for mega fans of the series too, this can be looked at as an extension.