Well, you know that you are going to get the answer of "try one and see!" Now, having said that, the G 21 uses a double stack magazine to get 13 rounds as standard. The grip is a tad large for some people. I don't perceive me as having anything special in hand size...rather normal...and I have no issues with the G21.
I have had two of them, a gen 2 and a gen 3. Both were 100% reliable. I currently do not have one, but will again soon. They seem to really hold resale well, and you can get a used one, shoot it as much as you want, then sell and try something else and always come back to it. I just sold my gen 2 model and am picking up a CZ 97 tomorrow to try.
I have a CZ 75SA that is incredibly nice and accurate, and I wanted to see how the model 97 stacked up against the Glock.
However, the G21 is a tremendous gun...very mild recoil for the caliber, fun to shoot, uber reliable. Try one out!