A book in a similar vein is "A Grand Unified Tour of Theoretical Physics", by Ian Lawrie. While I admire Penrose's book, I believe Lawrie's is written at a more consistent level and is probably more accessible to many (though not all) people.
the author of this comment and book recommendation is an accomplished professional physicist of no little reputation. Apparently he does not want to toot his own horn here on this site, so I'll do it for him.