It's somewhat rockier than "Year Zero", and not quite as electronic sounding, but the songs fit together and build a cohesive whole. Two favourites are "Echoplex" and "Head Down", both of which are brilliant compositions, and signature NIN. The instrumental "The Four of Us Are Dying" is also fantastic, and actually close to the sound of Massive Attack. And "Demon Seed" is moody and groovy as hell. It's hard to compare "Year Zero" and "The Slip" quality-wise, but suffice it to say that you really should have both. The latter is a bit funkier and more electronic, whereas this has more energy and is perhaps more focused.
I take my hat off for Trent, who has created his own musical space with a sound of his own, a new found love for his music machines and new ways of distributing his music. He's paving the way for other artists, exploring and innovating. Kudos.