I have a Gen4 20, it shoots very well. I'm not a rabid 10mm fanatic, but I will admit that it is a very good cartridge even if it is somewhat over hyped. I load my own which is darn near a necessity for the 10mm, but I can't complain about it much.
It is what it is I guess, nicely accurate and fun to shoot. I have a .40 barrel for it too (KKM) and it's a tack driver. Overall the 20 is a fine model, maybe not my favorite Glock, but it sure isn't the worst gun I've owned either!
Glocks and Single Actions!
Praise Yahshua Ha Mashiach!!