[Chazar]

I think the most distinguishing* feature of Dom2 for me is the combination of turn-based and simultaneous movement, so I would say something like:

A complex turn-based fantasy strategy game, which allows fast gameplay due to simultaneous movement.

It's more like a Real Time Strategy game where you have plenty of time to think through your moves and where you do not need quick reaction capabilities...

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(* I think that WarlordsIII became popular because it allowed simultaneous movement in multiplayer, thus allowing quick Online games. However, this also required fast reaction and so was rather RTS than turn-based, wheras PBEM games were never ending at all...)