Oracle is a very well-told story roughly following the life of Alan Turing, with SF elements added to explicate the story. Richard Stoney is being persecuted for his homosexuality, and is rescued by a mysterious protagonist. The highlight is a very rigorous intellectual debate between him and a well-known fantasist, John Hamilton. I give it 3 stars
Egan is right up there with Ted Chiang as the best hard SF writer currently active. He includes thorough explanations of seriously abstract mathematical and logical topics, much like in the Golden Age but with far more art to them. You feel like you could pass an upper division logic course after reading one of his books or stories. That might mean they are not for everyone, but they are for enough that he's won a Hugo and gotten eight other nominations. My favorite of his so far is Dark Integers, where mathematical proofs are used as a communication device. That one has the "could really happen" feel to it that the above story lacks in order to be really good.