In Warcraft, one of the best strategies for humans are mass caster. Combined with blizzard, stormbolt and thunder clap it can annihilate virtually all opposition.
Against ghoul, I sort of like storm bolt though. Storm bolt kills the enemy one at a time. Combined with bash, you can keep a metamorph demon hunter dizzy for the whole battle.
However, this strategy has one weakness. What about if enemies use a lot of air unit?
Mountain king is always my last hero. Meanwhile, I always sacrifice a peasant or two to check out what enemies are building. If enemies are building a lot air units, it's time to beef up your troops with flying machine.
Combination of flying machines, which is an anti air counter, with mass casters are awesome.
The sorceres can slow or even polymorph many expensive unit. while your flying machines attack the annoying hypogrhyp raider.
Can this be countered? One guy beat me up with a lot of hypogrhyp riders and chimera. That's the only way I know how to beat it.
I can combine this strategy with double expansion strategy. However, I find it more useful not to build expansion.
So, quickly build altar, farm, and make peasants untill your food is 18. Build lumber mill and tower.
Then upgrade your town hall. Harass enemies if necessary. You can use water elemental or blizzard.
If there fountain of manna you can use both blizzard and water elemental.
Then build priests, sorceres, and paladin. Quickly upgrade your town hall to castle.
Scout with your peasants. Check out his enemies. If it's ground unit, keep pumping out casters. If it's flying, then quickly build blacksmith and 2-3 workshops.