The reviews are in. Generally speaking, the gameplay/game design tends to be be praised, the simplistic, morality systems and story complained about. Happily for Infamous, its an action game, so the reviews are overwhelmingly positive. The length of the game the reviewers played is 15 hours (per side).
There is a day one patch (not factored into reviews) that adds what Sucker Punch claims are 5 hours of additional content. For the full details see Solid's post (fourth post in this thread).
Screenshots and Gifs stolen from Dualshockers (who stole them from the GAF).
Gamespot - Second Son focuses on pure enjoyment. It communicates that through the excellent combat that forces you to concoct crazy tactics to overthrow the invading forces. It draws you in further through its incredible visuals that not only hint at the PlayStation 4's impressive power, but employ a sensible artistic touch that makes Seattle a place you want to explore. It uses a complementary score to underline dramatic moments, and the sound effects pop with flair. And yet, for all of the elements in which Second Son excels, the narrative fails to carry its share of the weight. Still, don't become mired in the negativity as Delsin so often does. Instead, just laugh at the cheesy dialogue and chortle at how extreme the morality system is. Second Son is a great game that knows exactly what it is, and sucks you in with its unfiltered fun. - 8
IGN - Open-world superhero action games are about freedom and empowerment, and in these regards, Second Son is really impressive. Seattle is a big, beautiful playground for you to stomp around in with a set of devilishly fun and powerful toys at your disposal. It plays great, and it looks even better, but its advancements also beg it to be held to a higher standard, one that its overall story and morality systems struggle to reach.8.5
Eurogamer - Overall, it's good clean fun - so it's a shame that Second Son suffers from a consistent failure of imagination in how it's put together. There's not been much of an attempt to shake up the mission scenarios or structure of the game, leaving you with a very rote open-world adventure. Follow the waypoint marker, chase the suspect, investigate the scene, wipe out the jackboots; hunt the collectables and tick the boxes. You've been here many times before. The collectables and side missions all contribute to reclaiming districts from the DUP, which organises them into chunks and structures the reward usefully, and they've been judiciously pruned - but this is good admin rather than great game design. - 7
Destructoid - Second Son is by far the best inFamous yet. If you're a fan of the series, then checking this one out is a no-brainer, and if you're not, consider jumping in with Delsin. You don't need any prior knowledge of the franchise to do so, and if you have any appreciation of open-world superhero games, you'll enjoy it. - 9
Kotaku - Second Son doesn't just do shinier versions of the things previous Infamous games did. It multiplies and extrapolates on those things, letting them intertwine in really satisfying ways. So you get some skills that have choice built in, like sniping that lets you automatically go for headshots (evil) or hobbling (good.) You're a hero—or anti-hero, if you so choose—who can change the nature of his super-ness on the fly. There's a brief sequence in the last third of Second Son where Delsin's powers glitch out. You're forced to run past folks getting beaten up and you can't help. It feels pretty horrible, at least if you're playing Delsin as a good guy. That feeling is testament to how much the game pulls you in. Second Son feels like a game made by a studio reaching the peak of its own powers, on a new console that it's helping come into its own. - Buy
Dualshockers (they are a fansite, but one I use often so its only fair to include them) - To me, “next-gen” means seeing and experiencing things that weren’t possible in the last gen. This is the first game I’ve played that has convinced me that it could ONLY be fully realized with a current gen console. Tech babble aside, this a great and extremely fun game to play and replay. It isn’t 100% perfect but any gripes I had were overshadowed by how brilliantly designed the game as a whole was. inFAMOUS: Second Son is easily the best game I’ve played on the PlayStation 4 and the best example out there of how amazing the current gen can and will be. - 9.5
Polygon - I struggled with feeling let down that Second Son isn't a brilliant shift for action games. My small disappointments come mostly as a result of undeveloped potential. It had a chance to be a superhero game about more serious issues as well as a showcase for the power of the new generation of consoles. Instead, Second Son is more of the Infamous I already loved last generation, prettier, with more powers and better writing. But Second Son still kept me excited to discover each new power set and happy to shoot fireballs at fascist thugs long into the night. Maybe it's not so bad to just let go of responsibility and blow stuff up once in a while. - 8.5