Real Time Shields, or RTS, may look simple, but it makes you think and act on your feet. Basically, you play as defenders and form a phalanx around a city to repel attackers. Sounds simple, but there's a lot more to it.
Players have to be constantly aware of incoming attacks, and where the enemy will come from. They also have to be aware if the formation of their phalanx is enough to cover a city, or if any gaps will allow opponents through.