The game is composed of 3 parts. An adventure part where you speak to characters to obtain information (expect scenes from the show), exploring a map and taking control of a Knightmare.
Story will be the same and you will be able to use the Geass by speaking into the DS. There are various commands that Lelouch can give out and one of them is "Jiketsu shiro! (Kill yourself!)" You'll need to plan out what commands to give out to the enemy. Your team members can also be moved via simple voice commands such as "Kita da! (Go north!)". Sometimes they will not obey your mysterious voice and you'll have to make them collect some items. You basically have to guide your characters to the end goal.
Knightmare battles take place when you encounter enemies. You give out commands from the touch screen and you can shout out a team member's name to ask for support.
Looks bad... Wasn't really expecting anything amazing anyway. Hope the PSP and Wii games are better.
- Official Site