I'm not sure where to place the blame for the awful pacing, but the movie is just unrelenting. There are times when things should wind down, but then it's just more noisy stuff happening. For example, at one point a character is in need of specialized medical attention and they find out it'll be a fairly-long and "treacherous" trek to get it. The character is then cured within 1-2 minutes of runtime, the trek portion being a few seconds of that, then we jump straight into some exposition, then we jump straight back to what we were doing before, presumably after a long and treacherous trek back that also happens instantaneously. To get an idea of how jarring this feels, imagine if Gandalf told Frodo about what it would take to destroy the ring and the next scene was at Mount Doom.
The direction is mostly just odd, and I have no idea if it's because the director couldn't figure out what was happening in the script or because someone was meddling with his work.
Finally, the CGI monsters look terrible. There are some impressive uses of practical effects, but the transitions between those and their CGI counterparts are blatant.