Unique enough to attract an audience yet familiar enough not to confuse, it’s no surprise that it found an expansive and devoted fanbase.
Make a castle, defend it and knock down someone else’s), well executed. It did it with nothing more than be a good idea (i.e. Ask our colleagues in Germany about it and you’ll receive a voluminous response. As far as a games go, it’s been an incredible success. It’s easy to underestimate something like Stronghold.