The problem isn't the highlights of it - it's the low-lights, which make up most of those books. The main POV character is incredibly annoying to follow around - he's a dense, not-too-intelligent, but incredibly-long-winded everyman, who is never told to shut up by anyone around him.

I don't need an everyman perspective[1] on an epic science-fiction story! I am an everyman! I can form my own opinion of it!

They are also rather heavy on author-dictated philosophy (which is not particularly interesting, or insightful, and manages to fall flat in a pretty major self-contradictory way) - whereas the first two Hyperion books have much less of an author's voice in them, and are much more of a presentation of an interaction of different, competing value systems. That is interesting! Listening to the chosen one go on and on about choosing again (when none of their disciples actually do) is not!

The overall plot of them is fine. It's, unfortunately, all in the execution.

[1] Or at least, not one that's hammered into me for ~60% of the book.

Endymion and Rise were to Simmons what The Dying Earth was to Silenus. ;)

They're sequels set in the same setting, with a few cool ideas, but the literary flair -- the magic -- just isn't there.