Some people don't like the grip angle.
Some people can't get over the manual safety. But if you have shot a revolver....they lack that feature
Some poeple don't like the sights, but this is a problem that is easily resolved.
Some people don't like the way they look. (Why are you buying a handgun? Looks, or performance?)
Some people think that they Kaboom more. But I think that the higher number of kabooms has something to do with the high number of guns in circulation (more guns=more probability of a failure happening)
Some people don't like the fantastic plastic. Again....they have prooven to be reliable.
Some people don't like they way they fit in their hands. You can't know till you try one...everyone's hands are different.
I think that the frame on the full size .45 is too big, and I have big hands, but what I like in a grip may not be what you like.
Personally I didn't like one experience I had with a G22. I was qualifing for a police department (pre-hire) and the G22 that they had me use rubbed my middle finger of my dominant hand (right) raw a the the middle joint. I believe this is because the seam protruded and the recoil of the gun abraded my skin. I had a personal G22, and I never had that problem, and it could be easily remedied by running over the area with a dremmel or a fine grit sand paper so that the seam was flush with the frame. It was a fault of the maker, but a 5 minute fix that nobody would know you did (if you didn't go hog-wild with the dremmel/paper).
I like glock guns. I like that they don't have a safety (one less thing to fail/forget about in the heat of the moment). I like that they don't have an external hammer (for CCW) because you can't catch something that isn't there on clothing, etc. I like that they don't have that stupid lawyer lock on them. I like their tennifer finish. I like the trigger (it's the same every time, and with the grip angle and low bore height, the recoil makes for very fast and accurate follow up shots--at least in my experience). I like that there are cheap factory mags that are ultra reliable. I like that the gun is prooven to be reliable. I believe that there are two types of handguns. Guns you trust your life to, and guns you own because they fill some sort of sentimental or asthetic appeal. Glock is a gun you can trust your life to, but is rather ugly. Again, it depends on why you are buying a pistol.