Operation Chimera is a more polished exercise.
Rainbow Six Siege has begun Season 3 with the Operation Chimera DLC, and while the headline is the two new operators and the Outbreak co-op modes, the DLC also brings with it a lot of Quality of Life improvements that really help the game feel more polished.
PC players with machines that can just barely keep up with the game have the option to turn off any signal processing, instead taking the raw mouse and keyboard input and offering a smoother mouse movement.
Finally, a desync error that would keep a downed player from taking damage has now been fixed, but the biggest changes revolve around the act of reloading. The game will now remember which part of the animation you were at should you swap away, so if you ejected a magazine before going to another weapon, when you switch back, the game should know that. The exact moment that the ammo count updates after the reload animation has also been made faster and more consistent.
Full patch notes can be found here.