I don't like the design of the unit itself
Warning - Unnecessary (and probably irrelevant) subjective design rant below
Here's my big problem with the PS4 design from day one (which continues with the Slim/Pro): The ports/connections in the back are literally hidden from top-down view by the angular design when attempting to plug cables etc. I have my consoles organized in a relatively narrow stacked-shelf design, and making any changes to a PS4 console is maddening; the only view I have is top down due to the shelf/cabinet design, and the shelves are too short to lift/angle the PS4 high enough to be able to see the ports. The only real alternative is to pull the unit/cables all the way through the shelf to plug them in outside of the cabinet, but then I have to consider the length of cables I own for each console and make sure they're positioned vertically to accommodate any limitations.
It's obviously the firstest world problem ever, but what really bugs me about it is what Sony says about why they went with this design:
Seriously?. They actually identify the problem I state above as a benefit; the other functional benefits they use to justify the design are equally nonsensical. Just admit that you designed it to look distinct and stop pretending that the resulting shape has any functional benefits. The most common interactions that any consumer ever has with the console are (1) plug/unplug cable, (2) power on/off, (3) insert/eject discs. None of those functions benefit from the design in any way, and I would argue that most of them actually suffer for it.
Edit: In the interest of being more relevant, I am ultimately happy with my PS4 Pro purchase. The main games I'm playing atm (Titanfall 2, Battlefield 1, and Infinite Warfare) all have noticeable (to me) improvements at 1080p, and I'm looking forward to playing the upcoming Pro versions of FFXV and Nioh. I'll probably buy a 4KTV early next year, but I don't feel bad about paying for the upgrade early based on my experience so far.