I also thought it was a rather underwhelming reward. If the Speak with Dead spell was a reward just for assembling the book then I suppose it'd be a fitting reward since it requires you to explore two separate optional areas as well as defeat one of the more dangerous monsters in the first act of the game. The spell by itself would be a neat little reward since it'd give one of your characters permanent accessibility to the spell meaning you wouldn't have to carry the amulet from the very first dungeon around for the entirety of the game.
...But this is not the case. Instead the spell is locked behind three brutal DCs that you only get one attempt at. Failing at any point makes you unable to retry deciphering the book and gives you a permanent negative status effect. I suppose you could just leave the book in your inventory until later in the game where you might have access to more skill modifiers, proficiency bonuses and so on. But I feel that the longer you hold onto the book the less meaningful the reward becomes since it means you'd have to continue relying on the amulet or a cleric.
I think they either should reduce the brutality of the skill checks or add a greater reward for passing all 3 checks. However this seems like a bad course of action since they seem to want to avoid situations that'd leave to save scumming (I'm basing this on the recent IGN interview where Swen Vincke talked about their analytics picking up quest locations where they find a lot of players reloading their saves) which many players will feel compelled to if the reward is too lucrative.
Another option you have when opening the book is giving it to one of your companions instead. Some of them will accept the book, but I don't know if this actually does anything. Their dialogue seems to imply that they'll keep it for later, but I didn't choose this option during my playthrough so I don't know if this leads to them eventually uncovering the book's secrets somewhere down the line.
All things considered I feel like the book and its associated quest remains shrouded in mystery. I suppose it's fitting for the book, but I'd really like to know what exactly all the fuzz is about.
