Consider Phlebas is hard read, and considered the weakest book in the story.
Excession is probably the most different one, as a lot of it is essentially email logs, and doesn't deal much with the utopian elements except as far background (a lot of the main characters are at least a little eccentric from Culture point of view).
Look to Windward has a lot of the Utopia, but is IMHO quite good read except maybe for some of the chapters happening outside of Culture. Use of Weapons happens pretty much entirely outside of the main Culture body.
Try Excession. I agree "Consider Phlebas" may not be the best one to start with if you're not familiar with The Culture already, and even then it may be a bit hard to get through.
