Alright, EXTREMELY preliminary thoughts I jotted down while unpacking it:
R1 & L1 are a little awkward to get to, but the rest of the controller is fantastic. The sticks especially feel MUCH better than the DS3.
The supposed wobble issue is just people looking for problems. You have to press pretty hard on the corner to get it to move, and I can't really see how that would be an issue during normal use.
I like the power light strip on top of the console, very cool and futuristic looking.
I like how far apart the USB ports are. My USB stick is kind of wide and there's still plenty of room for both it and the DS4 charge cable to be plugged in next to each other.
The shape of the console is definitely much more attractive in person. Still wish it weren't so long and narrow, but the length is hidden where I have it so it's not really an issue.
OMG the d-pad is amazing. The edges of the DS3's d-pad would sometimes hurt my thumb after a while, but the indentation in the middle of this one cradles it perfectly.
The on-screen keyboard has no indication of what the backspace button is. I knew it was X just because I've used the PS3 enough, but it's still odd.
Can't sign into PSN, so I guess that's it for the night. I was going to post a direct screen capture, but I guess a camera phone shot will have to do.
And now I'm off to bed.
*Edit* - One more thing: make sure to go manually set your color range to Full if your device supports it. Mine was incorrectly auto-detecting Limited, and when I manually changed it all the colors got much more vivid.