Reliability. If I can't get through hundreds of rounds at the range without any issues then how could I trust it for the 3 rounds that I might actually need one day?
Lack of manual safety. I have done training classes with and without safeties. Many times I have pulled the trigger and after a moment of disappointment disengaged the safety and pulled the trigger again. Training for it only works if you will ALWAYS have guns with manual safeties and I can't promise that.
Point and Shoot accuracy. For some reason the way my hand/wrist work I can point and shoot anything that has nearly a 1911 geometry pretty well. But when I draw a Glock I am always off and have to adjust the aim before I pull the trigger. Something about that angle is just off for my hand/wrist. So when choosing a potential carry gun I need to draw and see how far off the sites are before I adjust aim. If that is too far off then the angle is just wrong for me.
Weight/Size. No matter how great the gun if it is too heavy or bulky then I might not carry it as often as I should. Any gun that is with you is better than the one you left at home.
Capacity.
Market Support. Must be able to buy mags, holsters, .....