One of the books is kinda cryptic IMO, but then again I didn't really try very hard to figure them out - I was ready to just look it up.
As far as being worth it, I think the true ending is much more interesting than the "bad" one. And that final boss...yikes. That thing is H-A-R-D. I was rewinding like crazy, and didn't think I would make it (I was at one hit left w/ no healing for a while at the very end, rewinding constantly to take back that last hit & try to avoid it). I have no idea how people ever beat that thing w/o the rewind.
Overall I really enjoyed the game. It's miles better than Circle, tho I still think the DS games I've played - especially Portrait - edge it out. And no, it doesn't touch SotN IMO.
Still, it was a worthy game in the series and I'm glad to have finally gotten to play it.
A few random stats of my playthrough. I believe in the end I was lvl 50 (would have to recheck, but it was definitely 50 or 51). My most-used attack soul in the early game was Ghost - it hit hard, tho it did often just veer off into the wild and not hit anything.
Mid-game I switched to Disc Armor and stuck with it for the most part for the rest of the game. For passive I used the Luck boost way too much - especially after reading towards the very end of my playthrough that it doesn't make any real difference in soul drops. Around mid-game I started using Headhunter a lot, since at that point it gave me a pretty significant boost to my stats. The middle soul ability I really didn't use a whole lot beyond the Flying Armor & Giant Bat abilities.
And I need to give a shout-out to the worst room in the game, that conveyor belt / spike / medusa nightmare. Just...no.
Also - is this the only Castlevania to not use the traditional sub weapons? (axe, cross, holy water, etc.) I will say, it KINDA makes sense when you get the true ending, but it was still odd. Especially since the hearts still dropped (and I guess they give you a little bit of magic back, but not a lot).
I agree w/ Izzy on the music - the music kinda sucks on the GBA anyway, but none of the tunes really stuck with me. I liked the mellow underground music OK, but again, Symphony it ain't. And it isn't a pretty game, but again, that's mostly due to the GBA. Honestly, SotN is such a step-up in pretty much all aspects compared to this game that it really feels like this game should have released first. Again, it's definitely not bad, I had a lot of fun with it - it just compares poorly.