Extreme plays pretty much the same as other Stronghold games. You have a small keep and some natural resources around you. You build structures to harvest the resources, which you can turn into manufactured goods and weapons. You give the weapons to your peasants, and they go smack a fool. And then, a winner is you.
If you?ve done it once, you?ve done it a thousand times, and other games in this genre (*cough* 1701 A.D. *cough*) are far better. If you?ve waited with baited breath for more Stronghold Crusader missions, you ought to pick up Extreme (and finish your master?s degree in WTF-is-wrong-with-you-ology). Otherwise, let this one fade from the store shelves in peace.
