First of all, let me say that I may be biased on the matter since I am such a huge fan of the Atomic Robo comic books. Seriously, if you don't know it, go have a look.
But even if you have never read Atomic robo, this iteration of Fate Core may be the one to have read if only one.
What I like most :
• the character creation is really easy and quick, thanks to the modes, but you can still take time to tweak your character to the finest details
• the comic strips illustrate splendidly how the system works
• the brainstorming mechanics is something I now use in almost every Fate game, injecting more storytelling games feeling into Fate
• the Gear system is also reusable in most settings where equipment is important to the fiction.
What I like less :
• This is really minor, but I would have liked the pregen characters to be one character per page, so I could have just printed them as handouts for quick games.
To the point, if you had to get only ONE Fate Core product, that would be it !