I keep hearing recommendations for the Culture books so I tried reading it recently and it just didn't work for me -- I gave up on it halfway through, which is rare for me.
They are a slow burn, but the ends always justify the means with those novels. If you really did make it 1/2 way, I’d encourage you to go back and finish reserve judgment.
My reaction is perhaps summarized by the old quip: "This is not a novel to be lightly tossed aside. It should be thrown with great force.".
It wasn't any one thing but I eventually hit a point where continuing just wasn't worth it for me. There's too much else on my to-read shelf which is less likely to seriously annoy me.
Me too with Consider Phlebas. Then I hit the Alastair Reynolds novels pretty hard and now I'm stuck for new material. Dune is en vogue so perhaps that's the right read next? I really enjoyed Vernor Vinge's A Deepness in the Sky but couldn't quite get into A Fire Upon the Deep but it still sits on my shelf taunting me.