Defense Grid is exactly as the name implies, a tower defense game. Doesn’t vary much from your typical Tower defense where you are given restrictive resources to build towers to defend your cores against an onslaught of different attackers.
World war one Verdun is a multiplayer only first person shooter set in the western front of world war one. Maps recreate some of the major battles fought historically with up to 64 players at time. Combat is brutal on the new players, you may want to try the cooperative defense mode to get started.