Character Creation
Character Creation from Soulcalibur III returned in Soulcalibur IV. Instead of including original weapon styles for use with certain classes of fighters, SCIV now only allows players to simply choose which character from the series they would like to have their created character mimic (excluding Algol, bonus characters, and the Star Wars guest characters). This differs from Soulcalibur III in that many unique styles were also included, such as Grieve Edge, Katana and Shuriken, Wave Sword, Steel Fan, or Tambourine. Many styles were removed in the transition, and the character creation has been simplified.
A wide array of new pieces of equipment are available for use in SCIV's Character Creation mode, and new options include a wider range of character voices (now with pitch adjustment) and the ability to change a character's general physique and muscularity.
In addition, equipped items now also affect a character's statistics. Armor, weapons, and accessories may increase health, attack or defense; they may also grant skill points that allow the character to equip special traits that affect the character's playstyle.[3] These traits range from automatically triggered guard impacts, the ability to cause damage against a blocking opponent, or even a stat increase based on parameters such as an opponent's alignment or gender. Standard characters will also be able to be modified in this way to a modest degree, allowing custom costumes and skill sets to be used in Special VS. mode. Custom characters can still be used in Standard VS. mode, but without any of the special abilities gained through equipment or weapon choice.
At the moment only one profile is allowed for offline versus mode, meaning that only one profile's created characters can be loaded at a time. If a friend comes over with their profile and saved characters, the only way to play with their custom characters is to either log off the other profile, or go through the process of recreating all the characters on the other profile. The game does not recognize two profiles and two save files, only one.

Active Matching Battle
Multi-fighter battles in Soulcalibur IV use a different structure from its predecessors, nicknamed Active Matching Battle (AMB). Similar to the tag system of games such as King of Fighters 2003, the AMB system allows players to switch to other members of a 'party' of fighters with the push of a button. Also, instead of starting a new round for each opponent defeated, new opponents will simply run into the battle immediately after a K.O. - with the exception of certain combatants. Matches utilizing the AMB system only appear in the Story and Tower of Lost Souls modes.

Soul Gauge & Critical Finish
Soulcalibur IV features an all-new Critical Finish system. Next to a player's Health Meter is a colored gem that represents the "Soul Gauge". The gem changes color when the player guards and is attacked. The color gradually changes from blue to green and eventually to red and then flashing red. The player's own Soul Gauge will regenerate if he or she makes an attack and hits the opponent (guarding or otherwise). If the character manages to empty out the opponent's Soul Gauge, he or she will get a short chance to perform a powerful Critical Finish move, which will defeat the opponent instantly, by pressing all four face buttons at the same time. Each character has his or her own personal Critical Finish move. Namco says that it developed the Soul Gauge to decrease the benefits from constant guarding, thus giving the game a faster tempo and making the matches more offensive.[4]

Force abilities
The Star Wars guest characters, Darth Vader, Yoda and The Apprentice, utilize unique attacks using the Force. Darth Vader is able to utilize Force-based pushes and chokes, Yoda can use the Force to launch himself into the air for complex aerial attacks, and The Apprentice is able to use Force lightning and other dark-side moves. These moves drain a special Force Meter, which recharges gradually when not in use. If the Force Meter is depleted, the player loses control of the character momentarily. At which time Yoda and The Apprentice show signs of fatigue, whereas Darth Vader appears to have malfunctions in his suit.[5]

Online Battles
For the first time in the series, Soulcalibur IV has the option to fight against other players online. Confirmed versus-modes available in online battles are "Standard VS" (for classic matches) and "Special VS" (for customized characters).[6] Created characters are playable in the online multiplayer mode.[7]

Characters
Darth Vader, the Apprentice and Yoda, characters from the Star Wars universe, are the playable guest characters. Darth Vader appears on the PlayStation 3, and Yoda on the Xbox 360. The Apprentice, the main protagonist of LucasArts' upcoming video game Star Wars: The Force Unleashed, also makes an appearance as a playable guest character on both the PlayStation 3 and Xbox 360 versions. However, recent videos that have appeared online [8][9][10][11][12], as well as Dale Nardozzi, Senior Editor of TeamXbox.com, confirmed that both Darth Vader and Yoda will eventually be made available as downloadable content for both the Xbox 360 and the PlayStation 3 consoles, respectively.[13][14][15]
Revenant,[16] Frederick Schtauffen[17][18] and several other minor Soul series characters make an appearance in battle; most can be made in the Character Creation mode.(information from wikipedia)