G21s are really great pistols. My favourite Glock was a model 21. I have long-skinny fingers and have skinny wrists, etc. I was able to shoot mine comfortably and didn't mind the recoil on the .45ACP round at all. For the most part, you may find yourself enjoying the G21 more than most other pistols. Something about the power of that round mixed with the un even balance of the G21 and its grip angle all seemed to make shooting it exciting yet easy. Ultimately I chose to shoot a different pistol for competition but I really enjoyed the G21 and one day may go back to one after trying a few other pistols chambered in .45 (of course always knowing that I can go back to the Glock - because it works, is incredibly reliable and shoots nicely).
Tim.