The Glock 20 is a pretty cool gun. 15rds of high capacity 10mm goodness. Great woods/camping gun. But 10mm is a caliber you have to understand in order for it to be a reasonable choice.
You probably made a bad choice if: You're going to go down to your LGS, buy some basic (Fed Am-Eagle) range rounds and JHPs, and treat it like any other range/carry gun. That's just not where it excels. And about 90% of factory ammunition out there is no different from your basic 40sw...except you get the privilege of paying an extra 50+% for every pull of the trigger, because it's "technically" 10mm...which is less common and considerably more expensive.
You probably chose well if: This is destined to be a woods gun, or you at least have a solid grasp on the caliber in question. 10mm is a caliber with tremendous potential. But it can only be unleashed if reloading or buying from the right sources (Buffalo Bore, DoubleTap).
I don't think it's a great carry choice for most folks, but that depends greatly on your environment. It can be a fun gun for plinking, woods carry, or even longer range fodder. Just don't make the mistake (that many make) of buying a 10mm, paying 10mm prices, and shooting ammunition that is literally nothing more than 40sw through it. Because in that case, you're just pissing $$ away, and you should have bought a 40sw.
"The Future is Unwritten"