I have had 6 now, rescues and the odd one from a puppy and they have all been hard to an extent 
They are loyal, loving and affectionate in my experience but I do think they need someone with a fair bit of experience in training dogs. They are needy, a little bit neurotic at times and live for their people. As a result they don’t tend to like being left alone and if they are they can find their own entertainment which often isn’t what you want! Personally I don’t leave mine for more than 4 hours or they start to become bored.
Exercise wise mine need about 2 hours a day. I don’t throw balls due to joints but I do give them toys and things at home to keep them busy.
The main issues I’ve had are around socialisation. Typically they don’t want to be everyone’s best friend and that’s just them, although I have had one or two super friendly ones generally they are quite aloof and can easily become reactive from bad experiences. Males also can go through a funny stage at maturity in which they can become dominant and a bit reactive and it’s important to train through this bit.
They will also ‘protect’ you from strangers or other dogs if they think you need it so it’s important to teach them from day 1 which behaviour you expect.
I take mine to training every week without fail, even the older ones not just puppies. I think it’s very important to keep on top of it.
They are generally a vocal breed and do bark a fair bit. They also shed ALOT. All year round. Mine have never been mud monsters though thankfully. I brush a long coat once a week and that keeps on top of it.
Mine have all been brilliant with children but most of them are quite herdy and will chase cats and small animals if they get the chance. They also have a tendency to loose it if the small child goes out of sight on a walk as they need to get it back to the group ASAP!
They are prone to many health issues. I wouldn’t touch one that’s not hip and elbow scored at the very least. I would also want DNA testing for CDRM as that’s an awful preventative disease. Epilepsy is common in some lines too so do your research.
Other things they are prone to are food allergies and skin allergies so I would suggest a good insurance policy.
Generally though they are lovely family
dogs but just not for the faint hearted. As long as you understand you are not getting a Labrador or a retriever temperament and you can’t expect it to behave like one then you should be okay. I’ve met so many aggressive and reactive ones that people have not had a clue what they are taking on, it’s generally genetic so check the lines and parents out very very carefully. If the bitch looks nervous in any way run in the furthest away direction you can!!!
Personally I’ve moved onto an easier breed
but I still have one GSD who is lovely but is harder than all of the rest of my dogs put together!!