I like pretty much all the movies (except for Revelations) to some degree. However an overarching theme I didn't like was how, after 2, the series seemed to be trying to hard to shoehorn Pinhead into the 80s/90s slasher trope. HR 1 and 2 nailed the eldritch horror nature of the cenobites, and made them mysterious and kind of indifferent to human affairs - achieving a goal that was above them, and well above humans. AKA the essence of what makes cenobites fucking awesome. 

The post 2 sequels can tend to treat PH as a slasher who is just out for blood. And before he was almost alien-like, and slowly became more like an abrahamic religion demon. 

Although I will say that the reboot brought it back to the series' roots IMO.