I kind of agree with you on that... and I kind of understand why.

The first book was an exploration of humanity in the stars. While there was contact, it had more the traditional science fiction footing that we're familiar with.

The second book was getting into the exploration of the mind and other minds. While the first book touched on the mind - with spiders being more relatable to how we think... the 2nd book presented us with something more alien in how the octopus thinks... and something even more alien.

The third book was downright confusing until the end and was more of a philosophy book about the mind. Can one mind be in two bodies? What entails thought? What is identity? ... and for that matter, what is reality?

The 2nd and 3rd books are good (and interesting) science fiction, but they go much deeper into exploring philosophy than many other science fiction books and use the scaffold of the universe to explore the mind rather than technological advancement. The upgrade of technology and how that changes things isn't the focus of the story - as one would expect in more traditional science fiction, but rather an exploration of a new mind. That change in the expectation from the first to the second (and third) book has some wish for more of that first book with the challenges of humans (as we can understand them).

Book 1 is a first contact story with survival. Book 2 is a psychological mystery about alien cognition (and a bit of horror to it too - "we're going on an adventure" gives me shivers). Book 3 is much more of a puzzle around unreliable narration and reality.

For me, I enjoyed the first book. I was confused by the 2nd book because of the change in the "it's not about the technology and survival anymore...". The 3rd book confused me on the first pass through it. The second time going through it and understanding where things were leading and being able to pick out the changes made more sense... even though I was expecting a book about the mind rather than science (the first pass through I thought it was more about the crow's minds).

Rendezvous with Rama