Even more so than The Picture of Dorian Gray, I struggle to call this a horror movie despite it being filled with monsters, skeletons, evil duplicates and a book of the dead. Unlike Evil Dead and Evil Dead 2 (the movies that precede this one in the series), Army of Darkness functions as almost pure entertainment and, I would argue, never comes close to even being creepy.
In this installment of the series, Ash has been sucked into medieval times where he lands in a court of Lord Arthur (ahem). He proceeds to help fight off the deadites that are infesting the time period as he tries to find a way back to the present. A pretty simple plot, all told.
The fun is in Campbell's delivery and the slapstick gore that surrounds him whenever he fights a monster. From battling a witch in an underground cavern to fighting off tiny replicas of himself, he always seems to be having fun and it is infectious to the viewer. The stakes never seem to get particularly high (except the end of the world, but this being a time travel story, we pretty much know everything works out ok) so it is hard to feel tension or, especially, fear. I don't think this matters to director Sam Raimi as much as giving his audience a fun time. And this delivers with boomsticks and chainsaw hands galore.
If you've seen the first two, you should definitely see this one. If you haven't seen the first two, why would you start here?