Of the ones I've read:
Gateway-Pohl: I hated this one, but that's because I generally dislike whiny anti-heroes. It was certainly ground-breaking for its time, and it's well written, but I couldn't get past loathing the main character.
Childhood's end-Clarke: One of my all-time favorite books. However, I first read it when I was 14, and I wonder if I'd think so incredibly highly of it if I encountered it for the first time now. Still, it's got some really beautiful big-idea stuff in it.
Rendezvous with Rama-Clarke: Enjoyable, but didn't blow me out of the water. Good Big Dumb Object exploration/adventure story.
Manifold trilogy-Baxter: Enjoyed the books individually (except #3 which really dragged), but hated it in total. You get to the end of all three books and discover that there was no real central driving force. The three books never really connect to each other. In the end it turns out to have basically been an exercise in (pardon the crudity), intellectual masturbation.
Man in the high castle-PK Dick: I can't do better than Randy M: "Thoughtful, a bit slow, but involving and interesting."
Stars my destination-Bester: Again with the anti-hero, I had a hard time with this one. However, it's connection to "The Count of Monte Cristo" was cool. A bit surrealist in tone, can be confusing.
Blood Music-bear: Not my favorite Greg Bear. I had trouble suspending my disbelief at the start (that a scientist would smuggle a biological compound out of his lab by injecting himself with it strikes me as on-beyond-stupid), and I never really recovered from that.
Contact-C. Sagan: Good, enjoyable, has some good science in it and doesn't cross the mysticism line too badly. I related to the protagonist more than would be normal (being myself a female astronomer (at the time, later switched to physics) with a close relationship with my father), so it probably spoke to me more than to others.
Flowers for Algernon-Keyes: Very emotional, very movingly written. Total classic; one of the few books I was forced to read in school that was worth it.
