IIRC it's actually five new stages. (Carrier, Desert, Forest, Tokyo Sky City and Lost World) You've also got new mechanics and moves for everyone, and new outfits. The real bonus, though, might just be Core Fighters. A F2P version that's compatible with the paid version should give the online a much-needed shot in the arm.
If you still haven't decided by now after seeing the new characters, new stages, new costumes, new modes, new online options, new moves, rebalanced characters, hearing about the better online netcode, and custom music(previous doa soundtracks) for characters, you need to pack it up.
Glad I pre-ordered mine in july.
Oh and I could have sworn Ultimate was announced a long time ago. Waiting until the last second to complain about the price instead of saving up was idiotic for some of you.