Ignore the mainstream reviews; this is WAY better than they would have you believe. The suggestion that it's nothing more than a stock-standard shooter, with little innovation, just prettier graphics, are incorrect. The graphics are definitely high quality, and the game runs at a silky-smooth 60 frames-per-second. But other gameplay mechanics and additions elevate Killzone Shadow Fall from 'just another shooter' to an essential PS4 purchase; if i hadn't already got a PS4, seeing this would make me want one. A big call, but it's a 'system seller'; worth buying a PS4 for (there, i said it!).
The varied single-player campaign consists of many different environments, which are large enough to provide plenty of ways in which to achieve your objective. The scan function that you can use to highlight nearby enemies, and the OWL, which is your flying robotic sidekick, are welcome features that make the gameplay considerably more tactical.
The OWL can be used to shield you against enemy fire, hack alarms, computers etc, provide a zipline for you to slide down from cliffs and high-up platforms where the drop would otherwise kill you, and attack enemies. There are lots of weapons to pick up and use, from standard machine-guns, pistols, shotguns etc, to more exotic variations.
Multiplayer is what you would expect from a modern shooter, it's robust, stable, and most of all, fun.
The whole game just oozes a level of polish and quality not seen from previous consoles, and should definitely be a PS4 game that you pick up. It's more than just a flashy tech-demo of eye-popping graphics to impress your mates with, and is well worth both your time, and your money.