Free Roam Policeman with GTA-level storytelling, Just Cause-level Scale and a detailed, life-filled New York City.
EDIT:
No, that's not true, my dream game would be a Spider-Man game with:
- a New York the size and street/level/pedestrian detail of GTA:SA
- a fighting system as orthogonal and in depth as Prince of Persia
- the useful and enjoyable school advancement (and social advancement) of Bully
- the web swinging with a few improvements of SM2
- the conversation trees and character iteraction of Mass Effect
- the physics system from the new Lucas Arts/"Force Unleashed"/Indiana Jones
- environments as destructible as Hulk:UD, except with 'knocked-thru-building' potential
- all the unlockables of Neversofts SM1 for the PS1 and then some
- Rumble-pack-only spider sense
- photography minigames of both Beyond Good and Evil
- contributing to the storyline AND Pokemon Snap
- getting points for unlockables
- Movie soundtrack guys on the sound team
- Next-Gen uber-graphics
- Being based out of a fully realized Ultimate Marvel New York City
- complete with Hot Coffee unlockable
- replaying comics 0-100 with some add ins
- some "Classic" Spider-Man missions
- Multiplayer Co-op and versus over live
- optional First person web swinging,
- 50+ hours of story with 10-20 hours of optional fun time.
Yeah... that's the gist of it...