The Glock 17L (along with the G24) is kind of the unicorn of the Glock line up. Produced in small batches and rarely, if ever, is it seen in the wild. :D Here's a quick review of mine:
-Reliable. The gun has had 0 malfunctions
-Accurate. The longer sight radius helps when targets get small or range gets long.
-Durable -Easy to maintain
-TONS of aftermarket support (not as much as some models however)
-Accepts 17 and 33 round factory magazines
-Glock's customer service is excellet
-Cheap replacement parts, should you ever need them
-Low Bore Axis combined with relatively long slide resulting in a soft shooting gun.
-Easily modified to fit the shooters' preferences
-Requires very little cleaning/lubrication to run reliably
-Many of the worries about brass to the face are assuaged; I've never heard of it with the G17Ls.
-Increased velocity due to the long barrel
-Not offered under the Blue Label or GSSF programs-Factory adjustable sights have a cheap feel
-Gold Dot +p 124gr: 1331 FPS, 487 FT/LBS energy
-HST 124gr: 1203 FPS, 398 FT/LBS energy
Here's a video with some shooting from the 12m line, a size comparison, and a chronograph test with some popular carry/defensive loads: