The best way to describe the final season of Castle is that it just feels off. It does use much of what made the show good to begin with, the case-of-the-week procedural format mixed with serial story arcs that run the course of the season. This season Beckett learns that the conspiracy involving Bracken, who was responsible for her mother's death, went deeper than Bracken, and she gets pulled back into that rabbit hole. As a result, she and Castle do not work together as much this season as they did in the prior seasons, so it misses a lot of the interplay between them that made the show great. As some may know, there were rumors that Stana Katic and Nathan Fillion did not get along behind the scenes later in the show's run (rumors are that they hated each other, although I have not seen either of them verify that). If valid, that did not affect the prior seasons, but it definitely seems like the dynamic between the two was different this season. Toward the end of the season, it was announced that should the series be renewed for a ninth season neither Katic nor Tamala Jones (who played Lanie) would return. Multiple endings to the finale were shot depending on the fate of the series. It was ultimately canceled toward the end of the eighth season and instead of ending on a cliffhanger, the series does provide somewhat of a conclusion for Castle and Beckett but does not really give a good sendoff to the supporting characters.
For those who get the DVD set, the extras include audio commentaries on select episodes, a blooper reel, deleted scenes, and a behind-the-scenes featurette. Okay for what is there, but not as much as the early season releases got.
Overall, the season is good, but not as good as prior seasons. As I said above, it just feels different in large part because the chemistry between Castle and Beckett felt off or lacking. The show includes a decent slate of guest stars including Fillion's Firefly co-stars Summer Glau and Jewel Staite, and an appearance by Oprah Winfrey. While I cannot say that fans of the show will like this season as much as prior seasons, I do think it is worth watching to see how the show wraps up.