Azaria Henson

Stronghold HD (the original) would be an excellent place to begin. It strikes a good balance between the game's economic and military aspects. It features a rather lengthy military campaign and a very short economic campaign. If you want a more military-focused game, Crusader HD (probably not extreme) is a better option. It contains a very lengthy "Crusader Trail" (80 different skirmishes), a cool Historic Campaign with sieges from the 1st, 2nd, and 3rd Crusades, and a skirmish mode where you may play versus AI. Following those two, Stronghold 2 is fairly nice, adding a lot to the construction features and changing several mechanics.