Not only did the final season of Durarara answer many questions the previous seasons left unanswered, it also managed to add quite a lot more to the plot line within such a small amount of episodes. While the OST isn't that great compared to the rest of the show, I'd say the story is a well-written and thought-through ending for this anime. Due to the amount of suspenseful in this season, I think it's one of the best anime endings I've ever seen. The last episode wraps up the whole show, just like it should.
The characters seem to have developed even further than in the previous episodes, and tend to show even darker sides of them, contrary to the cheerful start that we witnessed in the first season. Combine the character development with the usual action, comedy and drama of the show, and you get the awesome last season that's called Durarara!!x2 Ketsu.
Due to the fact I think this season is one of the best last seasons of anime I've ever seen, I rated this season a 9/10 in this review (and a 10/10 on my profile due to slightly biased reasons.)
Definitely recommended to watch, especially if you've got the time to watch it in one go.
