Permutation City is one of Greg Egan’s better-known works, and I strongly suggest you look into the rest of his ouevre which (aside from his Orthogonal trilogy) tends to be of a consistently high standard.
In general, I like the physics discovery books more than the books focusing on subjective quantum mechanics (especially Quarantine), although they are still well done.
To be honest I also found the concluding book of Orthogonal to be rather disappointing, but that’s personal preference.
I would have most certainly not drawn attention to the different nature of Orthogonal if I hadn’t had the feeling that the original poster is seeking for “hard sci-fi” that presents avenues for what our futures in this universe may be, as opposed to what other universes may be like.
I forgot it above, but I think Incandescence is the "our universe" counterpart to Orthogonal and it is quite good.