1. Superpowers. I need to enjoy, among other things, traversing the city (yay Spidey 2 and Prototype!)
2. RPG Mechanics. I want to grow my abilities--to do more than I could at first.
3. A unique art style. I'd love an art deco style.
4. Sidequests. I'm not talking boring, repetitive stuff like in Assassin's Creed (haven't played the second, so can't comment there) or Saboteur or anything else, I'm talking, like, between 30 and 50 unique quests.
5. Destructibility. I want to smash stuff. If I get into a fight with a giant naked ken doll that has a glowing iridescent sphere for a head that shoots laser beams out of it, I want to be able to punch him through skyscrapers, or maybe use a suspension bridge to tie him up!
6. Giant enemies. I think pretty much every 3D game could benefit from giant enemies. If you have superpowers and invulnerability, you sort of get bored, right? Well, not if you're fighting afro-wearing lizards the size of the Empire State Building!
7. Enjoyable NPCs. The biggest weakness of every sandbox game I've ever played is that I didn't care about any of the NPCs. That said, the only games that come to mind where I did care about the NPCs were Halo, Modern Warfare, No One Lives Forever, System Shock, Marathon... okay, so the list can get pretty big. If there are NPCs in the game, I want them to be awesome. A talking, bipedal tiger/pooka would be awesome.
8. Procedurally generated buildings. I'd love a city where the buildings are all randomly generated so I can go inside them and they're not all the same. If my character wants to go get a milkshake, he can. If he wants to go into a skyscraper and hide because he can't use his superpowers, and then this giant monsters is sticking its arm in and trying to grab him and he's like "OH SHIT!" it should be able to do that too.
9. Gender selectability. I want to play as different genders on different playthroughs.
10. Wacky bosses. I've already mentioned two. A living jello monster and a communist robot would be awesome too. All giant, of course. And lots of normal-sized thugs wearing domino masks, but using procedural generation to all look different. And maybe a fight on a living zeppelin. And a flying saucer.
Basically, I guess I just want something like The Power of Shazam! The game. I could fight ghosts and travel to the future and all sorts of stuff, and zap bad guys with lightning! Don't take my absurdity for a lack of seriousness; I would LOVE to play a game that has as much fun as I did this post.