GSD are very energetic, need LOTS of activity, and are very good family dogs.
See? We have two. :)
They couldn't be more different from each other. They're 7 month old brothers from the same litter, but Klaus is the more laid back guard dog type, and Ruger is the playful, goofy lap dog type. They haven't really chewed anything they're not supposed to yet except some shoes and a little of the trim on the staircase. We give them tons of toys, beef bones, antlers, balls, etc. so if they're ever doing something they're not supposed to we present them with other choices. THAT'S the key.
They need lots of outdoor time... walks, runs in the park, etc. Right now they're both enrolled in Beginner Agility Training just to give them, and us, something to do during the long Winter months. I've had lots of dogs, but none as smart as a GSD. Once you imprint something in them, it's there forever. They learn something in seconds, but everyone in your family has to be 100% consistent with whatever reward system you decide on.
As far as being a family dog, why not? Remember to SOCIALIZE SOCIALIZE SOCIALIZE as much as possible. We take them everywhere they're allowed to go. Klaus hates riding in vehicles...gets sick easy. But Ruger will hop in no prob. Klaus takes longer to warm up to other dogs, but neither of them has ever had problems with people. I didn't expect them to. Socialize. We're raising them with lots of touching... what I mean is, since they were 7 weeks old we touch their feet, tails, ears, snouts, etc. to get them used to it. That's how you learn YOUR dog. I do all the grooming...baths (which they hate) and nail trimming (which they hate), but I do it on THEIR terms.
Granted they're a dominant breed, so you have to take that into account. But as far as a family dog? Hell yes...go for it.
You want a protector? None better. Home security at it's finest. Want your face lick washed at 5AM? None better.
EDIT:
I've been trying to come up with some negatives to owning a GSD. The only thing that really comes to mind is the digging. Our yard looks like Omaha Beach on D-Day. They dig... a lot. I just keep filling the holes in and putting their crap in them to deter them. Worked with our last dog... not so much with these guys. If they want something, they'll dig for it.
Other negatives? I can't think of any. Except that now I'm going to have to replace our chainlink fences with 6' fence of some type. I'm afraid one of them will hop over the typical 4' chain link.
And there are health issues to take into account. We treat one for bad hips already, and the other scratches himself a lot. Some type of skin issue. It's manageable. The hip thing worries me though. He's just a puppy.