That instinct to guard/protect can go into overdrive, so early training with consistency is paramount. AND... that especially must include being around other (non-Shepherd) dogs to allow for them to learn non-aggressive body language, appropriate "greeting" behavior, and even play behavior appropriate to other dogs/breeds. If you go to a park and watch the other dogs approaching a shepherd, the latter is obvious. Well-trained German Shepherds will be interested in all around them, but do not become overly interested in other dogs, with their body language remaining neutral--to which the other dogs likewise remain non-reactive.
But, yes, they can be great dogs. I only wish we humans had not bred them so poorly to render most so prone to hip dysplasia and other joint issues.
More response than probably needed for a cute video, though. 
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