I'll offer some more tidbits here...
The guide is huge, over 250 pages long, but it's still sort of barebones. For example, it tells you where you will come across the Scrolls (many dead knights have them), and apparently a lot of the backstory is told that way. The guide also does not mention what is said dialogue-wise, or what happens in each cutscene. So even though there are lots of spoilers I'm able to provide from the guide, we will still be in for lots of surprises and plot twists I'm sure.
Also there are lots of puzzles & brainteasers. Many areas are un-passable until a big puzzle is solved. You will also have to rappel, swing, climb countless times to get into or over certain areas. Plenty of platforming for sure.
The giant spiders are important. The first one appears as a sort of mid-boss, but later they start to appear more often. There are also a few times you have to use them to gain access to other areas. You can jump on their backs and force them to knock down doors, and in one instance shoot a long web, Spiderman-style, across a chasm which you must then cross, walking on the web.