I have always sorta loved the GB. The only reason I don't own one is the trigger. When a friend sold his, I was getting out of DA/SA guns, so let it go.
Anyway, lots of experience with his. The trigger is quite mediocre also. Even SA, its sorta heavy. Not unreasonable, not gritty, but just needless.
The Gas Brake (get it?) is conceptually the same as the HK. A blowback, braked by the gas pressure. So what if its around the barrel instead?
The mag is "neat" incarnate. Alternate feed! Like an SMG. Easiest to load pistol ever.
Its big, but not super big. Like, not even beretta big. Its a full-sized combat pistol, and is not particularly wide or chunky. Rather slick gun, actually, I think. Nicely finished, but the crinkle-coat on some bits freaks people out. It was designed to be a service pistol (lost to the G17) so has some of that sturdyness to it. Presumably it would have been extended to a large product line and slicked up more if adopted; the first glocks were odd and junky.
Very reliable. Very, very accurate.
Can be very hard to clean. Stay away from lead, just like in the P7. My friend went to a dremel to remove the leading at one point. The P7 comes with a gas scraper, so this is apparently not unusual for this operating method.
After Steyr stopped production, they sold rights to it. Maybe... Ruger sold it as the Pi18 or something, poorly and with extra uglies, for a while even. Then others. Then it died. Steyr does this in general, apparently. E.g. the TMP is gone, but Bruger + Thomet is selling a nice PIP'd version of it again.