The three rogue specs share many common mechanics. They all follow the same formula: generate combo points, use finishers, activate your cooldowns when they come up. The real differences between the specs only show up once you start playing them. Assassination is well-known for being more relaxed and favors pooling energy over spamming attacks. Subtlety rogues have a knack for massive burst damage via their complex cooldown, Shadow Dance.
Combat is arguably the simplest of the three specs, and is often characterized by its fast-paced gameplay and high actions-per-minute rate. Adrenaline Rush, which has been combat's signature cooldown for years, is designed to let you push buttons even faster. Assassination's Vendetta lets you hit harder, subtlety's Shadow Dance lets you use openers, and Adrenaline Rush doubles the numbers of buttons you can push. Unfortunately for combat, the concept of "push more buttons" can't scale forever.