Infamous: Second Son doesn't exactly shake things up as much as refine the Infamous formula. It's a gorgeous looking open-world, superpowered playground that'll provide plenty of entertainment, and won't hit your wallet too hard now that ShopTo and Amazon have dropped the price by a further fiver.
To be honest, though, if you're planning on picking up the standealone expansion -- First Light -- I'd actually start there. It's over ten quid cheaper, and actually works best when played first as its prequelicious plot won't be spoiled by the things you learn in Second Son. Thanks to oUkTuRkEyIII @ HUKD!