I got 100% of the endgame collectibles yesterday so I think I'm done!
Honestly, some of the collectibles lowered my opinion of the game a bit. Some of them felt unfairly hidden. Many, felt like they were in the wrong game--as if the developer liked a particular style of secret in some other game, and wanted to include it in this game, even if it didn't really fit in.
I had to google for help with ~3 endgame things, I'm glad I looked them up, because they're stupid.
My opinion of the game peaked when I got 100% of the instruction manual, that would have been a satisfying stopping point.
People who don't finish their sentences
I'm a Castlevania superfan! Ask me anything!