Paragons is a strange beast. I absolutely adore this book, but I can't recommend it without a few initial caveats. First and foremost is that Paragons is not exactly a setting. It's a toolbox, albeit one with all the elements of a setting: a high concept (a real-ish world with mysterious superpowers, where the "Breakout" of paranormal ability is relatively recent), a whole boatload of organizations and NPCs to interact with, lots of adventure seeds, and the Imageria -- a spirit world/collective unconscious/paranormal enigma in which all of myth, legend, and story can be found in some form or another. Second is that the design of the book leans heavily towards being a source for GMs. All the information on the NPCs, including any secrets they might have, are listed right there in the character section, rather than separated into their own chapter as used to be commonplace. Finally, Paragons is almost ten years old as of this review -- the setting and concepts translate surprisingly well, but a few things stand out as anachronistic (remember when the TV series Heroes was the hot new thing, just before Iron Man changed the superhero landscape forever?), and it uses Second Edition M&M, so playing Paragons in 3e will take a little work.
All that said...remember when I mentioned loving Paragons? This book just oozes personality, somehow implying an enormous setting with a rich history without setting any of it in stone. For a GM who wants a semi-realistic modern setting with super-powers, a world of dark strangeness revealed, or a gonzo everything-is-connected framework to provide connections in a more four-color setting, Paragons can't be beat. Its organizations have enough detail to hint at complex, ongoing agendas while leaving plenty of room for GM development or reimagining. Every NPC is an interesting potential plot hook. The Imageria gives Paragons a unique flavor that keeps it from being generic, while having more than enough flexibility to serve a wide variety of different campaign purposes. Many of the forces in play are connected, giving Paragons a lived-in feel, while still managing to allow for the insertion or removal of characters or factions without disrupting the meta-setting's elegance. It's simply a master class in world kit design. Frankly, I would call it perfect were it not for the aforementioned lack of separation between player and GM sections.
There's a trend in superhero gaming that leans toward getting back to the bright colors and "anything goes" nature of old-school comics. It's a welcome move towards optimism and pure fun, and Freedom City staked out territory in that realm many years ago. Even so, there's still plenty of room for a more critical eye on what superhuman powers would do to, and with, real people. Further, not only is there nothing stopping groups from running a near-straight superhero campaign in Paragons, the idea gets plenty of support with the official UN super-team Vanguard and a few sample NPC heroes (though the Paragons plug-in found in Worlds of Freedom would probably help). Just don't expect the super-villains to fly around wearing spandex; that's largely a hero gig. Where Paragons shines is in the chance to do other things with superpowers, either instead of or in addition to old-fashioned rescuing. There are mysteries to solve, conspiracies to foil, tough questions to face, vast reaches of space and Imageria to explore, and the big question to which Paragons gives no definitive answer (while covering the most likely possibilities): just how is all this impossibility possible?
I cannot recommend Paragons enough to GMs looking for something unique in a modern setting. Yes, it takes a lot of buy-in, and much of the work is front-loaded, but the results will almost certainly be worth it. Paragons is a book and world that needs a lot more love.
As a final aside, much of the buy-in and early work can be minimized by borrowing from a few of the other "secret modern world with powers" books on your shelf. Mage (either), Shadowforce Archer, Feng Shui, Conspiracy X, just about anything with Lovecraft...all can be raided for parts, with groups and/or characters fitted into Paragons with a minimum of fuss.