As others have pointed out (especially Sevens):
1. Ergonomic grip angle and size -- can be customized by grip thickness, changing trigger length, etc. With a beavertail grip safety and a high hold, the pistol is very controllable under recoil.
2. A trigger that can be made absolutely great.
3. When made right, a very accurate pistol.
4. Very customizable.
5. A bit of mystique.
Jim's Rules of Carry: 1. Any gun is better than no gun. 2. A gun that is reliable is better than a gun that is not. 3. A hole in the right place is better than a hole in the wrong place. 4. A bigger hole is a better hole.