Counter-Strike 2

Counter-Strike has been iterating on one round structure since 1999: buy equipment, plant or defuse, no respawn until the round ends. That constraint is what makes it the deepest team shooter available, with a single life, every decision carries a cost, and the economy layer means the round you lose badly shapes the two rounds after it.

Counter-Strike 2 moved the whole thing onto Source 2, replaced the tick-based hit registration with a sub-tick model, and made smoke grenades into volumetric objects that react to gunfire and explosions. It is the same game underneath, which is the point. The skill ceiling remains effectively unreachable, and the learning curve is genuinely steep, expect a rough first fifty hours.