It's the only online game that truly requires teamplay to succeed in. Everyone has a role, where the unskilled can man turrets while the skilled can play fighter pilot. Warzone 2100 is the best traditional real time strategy game. Myth 2 or Ground Control are great. All these games are reviewed in our strategy section.
Subspace is the most skill driven game there is.
It's also free and in my opinion the best game of all time. Listed under action. Winzip comes in handy here.