Umm.. well, we have one. She'll be 12 next month. We got her when our youngest was almost 3, and the oldest was almost 6. They all grew up together. :)
Like any dog, you have to train them. And like any dog, it is best if you find one whose personality fits with your ability and personalities. Some GSDs can be extremely dominant and it takes a strong person who understands (and can carry out) the alpha position to train them and manage them well. Others are not like that.
Also, they aren't necessarily any larger than the size you say you are ok with (labs/retrievers). They are not *supposed* to be bred to the size of 100 lb dogs. It's not the recognized AKC standard to do that. Females should more typically be around 65-75 lbs. Ours is just under 60 lbs. We made sure to search for a smaller line.
Inside the house isn't an issue regarding size. She is very quiet (unless there is a reason to alert us to something.. sometimes cats in the trees across the way, but more often it's UPS, or FedEx or the trash truck *stealing* our garbage/recycling).
They require regular exercise, and you are likely to have problems if you don't give him/her that. They are intelligent and will get bored if you don't exercise them and provide them with activity that stimulates them mentally. We like to hide things (toys/treats) and have ours go find them hidden in the house. It's good mental stimulation.
As far as neighbors being fearful? Not been a problem for us at all. The only problem we have ever had related to perceptions of her due to her breed was when we were in the construction phase building our home. We had to rent temporarily, and many places just will not lease to pet owners. And if they do, they won't lease to owners of pets over 25 lbs. And if they do, they exclude GSDs, Rottweilers, Pits, Dobermans and other dogs perceived to be dangerous. We were lucky and found a privately owned situation with owners who loved GSDs in particular.
Not sure what else you want to know, except that they are known as German Shedders for a reason. :P
OH, and we LOVE her! LOVE LOVE LOVE. Will never choose another breed. Once she crosses the rainbow bridge, I'm not sure we'll be up for the commitment of another any time soon. But if so, it's be another GSD. Or maybe a pair, so they will always have company if being pet sit or boarded? Ours is a member of the family, but traveling with her doesn't work so well for us (we visit family and they don't allow pets in the house). So we hire a sitter for her. She is extremely bonded to her pack (us) and misses us. It's not separation anxiety... she is fine being left alone. It's just she misses us and gets depressed. Having two might help alleviate that.
--ETA
Just read Angela's response.
Ours is like that, too. She wants to be where we are. She loves being outside, but only if we are there. She will go outside to do her business, but comes right back in, or lies on the porch. She doesn't roam or *prefer* to be outside. (Well, the few times a year we get cold weather she rather enjoys lying outside on the porch, the rest of the time--which is most of the time--she prefers inside with the a/c and no gnats.) Not having a large yard isn't a deal breaker. As long as you still provide exercise. Long walks and some time off-leash to run full out are good. That's the only yard issue I'd see. Ours loves frisbees and tennis balls. Throw them, and she runs to retrieve and go again. Over and over. You can't replicate that on a leash or a sidewalk.
Our GSD has never been randomly aggressive. She even gave up her bed to my nephew with Down's Syndrome and went somewhere else to lie down. She loves and worries over small children. The only person she was ever aggressive toward (and justifiable) was a worker I had in my home who gave her a bad vibe and tried to approach her (and by default my 5 year old daughter) so she growled and barked at him and sat on my feet right in front of my daughter, and a plumber who crossed the living room towards me without my ok. (He'd been going in/out to his work truck from the hallway with no issues until he varied from this and was coming across the room towards the kitchen where he hadn't previously been invited.) She jumped up between us and barked at him. He stopped. I told her it was ok and went over to the guy, and she was happy and friendly again. Every worker who has ever come into my home it's a similar story. As long as they stay where they are expected, she observes from a distance (in between them and me, usually) and is pleasant. Not necessarily allowing them to pet her, but not being rude, either. She follows my lead (as most GSDs will do, follow the lead of their alpha). If a guest is brought into our home, she meets them, observes them and typically responds in kind to how my husband and I regard them. If we give them a hug, they are golden. :)