When the enemy can fire through walls and kill you from anywhere, it pays to be paranoid. To that, Siege adds an elegant dance of constant doorway-and-room checking that punctuates the game's sporadic firefights.
The Rainbow Six series has always been tactical, driven by delicate plans and surgical strikes. Previous Rainbow Six games were similar (Tom Clancy's gaming brand is pretty consistent as far as morbidity is concerned), but Siege mixes in so many unusual ways to attack through walls and around corners that make vulnerability an overarching theme.
Like Dark Souls and other hyper-lethal games, Rainbow Six Siege encourages an extreme level of caution at all times.
In the heat of an assault, this leads to a series of gameplay beats orchestrated by fear. Death and fear is a constant for both sides, and the fact that there are no second lives or chances – unlike the overwhelming majority of online shooters – brings your own mortality to the forefront. Even if the counter-terrorists manage to find their target during their reconnaissance phase, the defenders could adjust their fortifications and fan out to prepare ambushes. On the flip side, defenders are always entering a relatively unknown area. But make no mistake: something is always coming for you. Even the best reinforcements can be breached, if not with basic gunfire and brute force, then with thermite or specialized missiles. Defenders, holed up and comparatively secure as they are, never quite know when or where or how they'll be hit. Gameplay in Rainbow Six Siege strikes a special balance between the two sides.