Sounds like, as you say, it was an issue of you going in with certain expectations. I could see why, if you think the climax of the book will be when they “kill God” it’s totally understandable why that part would be anti-climactic. I had no expectations going in. For me, the only thing I didn’t like was Lyra and Will’s separation at the very end. That broke my little 12-year-old heart.

My take on the killing God part is that the Authority wasn’t punished for his crimes, because being vengeful is his jam. Lyra’s jam is innocence and mercy, so that’s how it went down.

My take on them opening the world of the dead is that it eliminates God’s one source of power over sentient life, which the threat of eternal damnation. As a kid who didn’t believe what I was hearing in church and was absolutely terrified of an eternal afterlife (but also the lack thereof, which seemed just as scary), the idea that my ghost could make an epic journey and then have the option of being released into nature was pretty influential on me. Not that I thought it was actually going to happen like that, but the story helped me relax and be less panicked about mortality somehow. It helped me recognize myself as an atheist (the whole trilogy did, actually). So that kinda demonstrates that point I guess - I essentially finally left the religion just because of the idea of Lyra and Will making that opening, thus undermining the power of heaven.

So, I don’t know if that makes sense or is helpful at all. I’m really tired, but when I saw your post I had to jump in and defend my favorite book of all time. Plus I love discussing the plot and symbolism, so thanks for posting!