Glocks are good, solid guns, and as reliable as any other semi-auto pistol out there. Don't get me wrong, but Korbin did ask for criticism of Glocks.
Glock's reputation for invincibility has a lot to do with Glock's habit of denying any and all problems while quietly doing "upgrades" (NEVER a "recall") on their guns when problems surface, and a horde of internet Glock fans who drink the cool-aid and think their Glocks are magical talismans that cannot break.
1. Glocks have a reputation for kabooms (blowing up). Some Glock fans say this is an internet myth, but it seems to be a genuine problem. Most likely due to the unsupported chamber and the polygonal rifling. It appears to happen more with .40s than 9mms.
2. Glock has had their share of malfunctions and defective guns, including:
- defective slide rails
- phase 3 malfunctions, where a fired case rim sticks under the extractor, and the case mouth simultaneously lodges at the mouth of the barrel hood. The standard, Tap-Rack-Bang drill will not dislodge it, and the slide cannot be manually moved in either direction.
- defective guide rods
- bad magazines which caused guns to fire out of battery
- The usual FTEs, FTFs, etc.
3. They're ugly
4. Their blocky shape makes them harder to conceal, in my experience.
5. I have never found a Glock that fit my hand well. The grip angle and shape are totally wrong for a significant number of shooters.
As a final note, I would NOT recommend a Glock as someone's first handgun. Not that it's an expert's gun or anything, but some guns give a little more margin of error than others for times when our gun safety is less than perfect. All of the Glock's "safeties" are in the trigger, which has led to a significant number of negligent discharges. Between the safety issues and the sort of utilitarian, mushy and uninspiring nature of the Glock trigger, there are better choices. If you have your heart set on a semi-auto pistol, I'd recommend a good .22, like the Browning Buckmark or Ruger mark II or mark III. Shoot it A LOT. Get good with it, THEN buy the Glock or whatever pistol fits you best.