Simplicity and reliability.
The best thing about a Glock is they will eat any ammo you put through them. I have never had any feed issues. The grip angle is different and people either love it or hate it. The other thing I like about a Glock is the tear down is very simple. I currently don't own one but have had several. I think they are very good guns but in my opinion there are better ones out there.
Glocks don't feel good to everyone. Buy what fits you best. But don't go cheap on a self defense gun.
I've never shot one and wouldn't pay $500 for a Glock. It always just feels like a hunk of timber in my hand. I'm sure they make different grips for them, but they're never on the gun in the cases. It just feels wrong in the hand and doesn't encourage me to look any further into them. What's the deal?