I can assure you from experience that this is far from a formality! The format is your standard final round: Interviews, group exercise and a written communications exercise, but make sure you prepare for it and can give a good impression of yourself all day. Only the slightest imperfection can prove to be your downfall.
This all sounds very daunting, but that's not how I mean it to be. Just make sure that you're on top smiley form all day, and try to relax!!
Good luck, Steve