The main problem with The Slip is that when it's good, it's good 90's NIN, and when it's bad, it's... Well, bad.
The way I look at it is, there's been a clear progression with NIN since TDS. The metal nihilism of TDS gave way to the haunting instruments and orchestration of The Fragile. This led to a more alt-rock, whole band NIN in With Teeth, seeming to clear Trent's head for the computerized, electronic Year Zero. After that came the totally instrumental Ghosts, which led to... The same kind of songs Trent has been singing all along. 1,000,000 would fit nicely on TDS. Letting You could slide in nicely after Survivalism on YZ, Head Down and Echoplex feel like WT tracks, it's nothing new. It's like a career retrospective told through B-sides.
Or maybe I'm talking nonsense again.