An exceptional season with greatly improved art style, animation, music as well as directions compared to seasons 2 and 3. Although the animation may seem a bit stiff from time to time, it's mostly quite fluent and smooth, and the music carries great emotions befitting of the scenes shown. This season introduced a lot more characters at once compared to previous seasons, and each one of them are given enough spotlight to shine, which is admirable. The story covered this time is also one of the greatest arcs in the whole series. For anime-onlys, this is definitely an extremely solid season, but people who have read themanhua would've spotted a LOT of cut or changed content (some for the better, but mostly a downgrade from the original), which somewhat leaves me slightly disappointed in that aspect.
Otherwise though, this season is arguably the best so far in the anime series.