-Reliable. The gun has had 0 malfunctions
-Accurate. For s subcompact gun it's relatively easy to shoot well.
-Easy to maintain
-TONS of aftermarket support.
-Accepts 15, 17, and 33 round factory magazines
-Glock's customer service is excellent
-Cheap replacement parts, should you ever need them
-Low Bore Axis resulting in a soft shooting gun, especially for the weight.
-Easily modified to fit the shooters' preferences
-Requires very little cleaning/lubrication to run reliably
-Carries well but you still have a 10+1 capacity.
-Most shooters will not be able to get amore than 3 fingers on the grip.
-Comes with a serrated trigger (even the US models)
Here's a video with some shooting, a size comparison with the CM9 & S&W Shield, and a discussion of the pros and cons of the gun.