I've almost certainly go too many books, but for me RPG books are two things:
- Something I do or plan to use the actual contents of. Whether that be rules, tools, or adventures.
- Physical objects that are nice to look at and hold.
Happily the indie RPG scene is very good at making books that cover both of those categies. I will once in a while go through the collection and give away books that I both don't think I'll ever use, and also aren't nice enough as objects to be worth keeping around.
I also have a number of magazine bins filled with zines, which I love but also desperately needs to be pared down.
Also because I will take any opportunity to share a shelfie:
Desk RPG shelf of "close to hand" stuff (and also tall books because they don't fit on the other shelves).
Ancillary bookshelf of RPG stuff:
I ran the first level of ASE (plus the gatehouse mini level) using a slightly modified Electric Bastionland a while ago. We had a great time, super fun to explore. But when my players find a way down to the second floor and I read ahead to see what was coming up it got, for my money, a bit too ridiculous.
We talked it over as a group and ended up dropping the campaign to do something else.
What we played was a ton of fun, and just that first book is a very significant chunk of dungeon crawling, but I just didn't want to run the weird clowns and such that the second floor introduces. Went from wacky and fun, to just over the top weird.
My one criticism of the first floor is that most of the "factions" are intrinsically hostile and non-trivial to try and communicate or parlay with. Sort of ran against the the usual mega-dungeon faction play, but it wasn't hard to tweak on the fly to make things work better.