Greenskins field massive hordes of cheap units that may individually be weaker than their counterparts, but collectively can overcome and defeat almost any enemy. They have a very diverse roster composed of a small number of sturdy elite melee infantry, a large selection of highly mobile shock cavalry and chariots, as well as powerful monstrous infantry and monsters, with a small selection of decent battle magic and artillery to top it off.
As a counterpoint, the vast majority of their melee infantry options are weak and only work as cannon fodder, their ranged options - be they infantry, cavalry or artillery - are inaccurate, they lack flying options, and their monsters, despite being effective in close combat, are slow and very vulnerable to enemy missile units. The Greenskins are all about overwhelming the enemy with sheer numbers and brute force, with the chaff providing cover for your heavy-hitters.