Paper kills the ability to quickly scan the feed for the 10 percent of stuff that might interest me even momentarily. I can either see one thing at a time with the stories full screen, or three things at a time with them in an awkward location at the bottom of the screen and one of them (for which there is a 90 percent chance that I don't want to see it) taking up the top two-thirds of the screen.
It's certainly pretty and with some content other than my Facebook feed, it might be a good interface. It would be perfect if I wanted to read 90 percent of this stuff.
But that's the whole idea. It's to keep you more engaged. But that's not how I use Facebook. I don't want to "engage" with it. I've got a million things competing for my attention and most of them are better than my Facebook feed. I want to get in, find the interesting stuff and then get the hell out. I suspect I'm not the only one.