Mine is "curved" on the back. I can spin the phone on it back on a flat table. Sounds like this is a common problem on these CandyShell Grip cases for at least a generation or older Speck CandyShell Grip iPhone cases from some review comments.
Mine is easy enough to get the phone in or out, but it still requires some effort if that makes any sense. That said, the phone stays really securely in the case and won't slip out under normal use.
This is my favorite case, but recently I've gone back to my Spigen Air Cushion just because that one is much slimmer and lighter, but not so flimsy. I did order a Ringke Fusion clear case cause of the sale, and the buttons are much easier to press than my Spigen one (when I tested on my coworker's).
I'm also tempted to try one Zoogue case just cause of the mostly positive reviews I've seen and the sale.