First off, technically not a spoiler but you should probably know that roughly half of this special episode is just a recap (of which I just skimmed through). I am pretty sure that nothing too important happened during that part that you didn't already see if you watched the first season. I guess the recap is fine if you haven't seen the show in a while.
Other than that, I quite enjoyed the remainder of episode. It was an interesting story, following the events of season 1. The animation I believe, was no different than prior episodes (in other words, as good as always). It's the same deal with the music; in this episode specifically, the music was used well in some of the really emotional scenes.
All in all, I feel it was a good episode and rate it a 7/10 across the board (not really including the recap, but I recommend watching it for the neat new content). Though, I do not believe that I will be watching the potential second season of the series.