Guilty Gear, subtitled The Missing Link in Japan, is the first game of the Guilty Gear series. Guilty Gear is set in 2D, similar to Street Fighter and The King of Fighters, but is fast-paced and focuses more on the use of combo techniques. The game features 10 characters and three hidden characters. It uses a six-button layout: Punch, Kick, Slash, H-Slash, Dust and Respect. Combat is one-on-one set in best-two-out-of-three rounds.
It uses a "tension" gauge, akin to Street Fighter Alpha's Super Combo techniques, in which characters can input certain commands and activate special-moves called Chaos Attacks. It also features an air-combo system, comparable to Marvel vs. Capcom's "Aerial Rave", allowing combos to be performed on airborne opponents.
Guilty Gear features instant kill techniques called Destroy Attacks, that can be activated after a Murder Outbreak attack successfully lands on an opponent, effectively ending the match.
The game also has a feature called Chaos Mode that is activated when a character's health is at the half-way point (yellow bar). A red aura will surround the character and he/she is able to perform unlimited Chaos Attacks.
Source: Wikipedia, "Guilty Gear", available under the CC-BY-SA License.