@AMetroid
@Nakanowatari
WN and LN are only really similar until the end of the first arc, which is the stuff with the church. Most of what happened back at Cal Mira is new and, even if the monsters where in the WN, most of what's happening now is going to be new. That includes the mysterious lady, the villain for this arc and how they deal with the source of the monsters. The next arc is entirely original. The arc after that is the next section of the WN with a bunch of new stuff again. After that is another entirely original arc. Then the section of the WN after the last one with a bunch of new stuff. Then an entirely orignal arc. (you seeing the pattern here?)
tl;dr
We technically broke away from the WN near the very beginning, but most of the differences where subtle and change the meaning and characters more than the actual events. However, everything after the fight with the pope is either mostly new or entirely new.
@samuel_maxis
Glass was in the WN too. It's just that she appeared the first time and didn't show up again until near the end of the story. L'arc and Thressa weren't in the WN. In the LN, they're all regular characters.