I'm finally getting into both discworld and culture. I've read a number of other discworld books before, two of the night watch, mort, I think another I don't recall right now. Now I'm reading The Colour or Magic. It's enjoyable but I'm finding I'm going a little slower on it than the others.
I also have the second culture book, Player of Games, ready to go when I finish the discworld book. I really liked how bonkers Consider Phlebas was (felt like a constant stream of chaos for the crew).