Misblamed: To an extent, Stephan Smith Collins failing as The Other Darrin. The way Pinhead sounds is just as much a part of his iconic presence as his look, but Doug Bradley doesn't sound like Pinhead either. Not only was the production too short on budget/time to bother with the usual post-processing that goes into Pinhead's voice, but the actor is dubbed over anyway.
Narm Charm: Revelations has a low budget that shows, campy acting from overcompensating actors, and a replacement for Doug Bradley playing Pinhead that couldn't be more obvious and distracting if they'd tried. On the other hand, the script is a genuinely clever Call Back to the first two movies that goes out of its way to adhere to their mechanics, characterizes the Cenobytes as the pure Sense Freaks they originally were without all the For the Evulz stuff, and puts new twists on old tricks like a victim of the Cenobytes trying to exchange another for himself only for Pinhead to find the trade worthless.
One of the reasons for all of the call-backs and references to the first film, is due to the fact that Revelations was originally conceived as a full-on reboot. The low budget and lack of Doug Bradley was due to the fact that they waited so long that the rights were going to expire if they didn't have something made within an ultra-ultra short period of time to get the film made and in theaters (where it played in a single theater as a free showing only once).
Although, Doug Bradley apparently didn't like the script (or at least the version of the script they sent him when he asked). That, combined with how little they wanted to pay him, was the reason he didn't come back.
To be fair, Bradley didn't hate the script either, he just found it to be unfinished. The problem he had with it was Dimension's refusal to make a second draft.
Replacement Scrappy: The movie could have been a well made success, and Stephan Smith Collins would still be seen an an inferior replacement for Doug Bradley.