I'm just making a list of what NES games would work well to make modern titles on the NES. I'd put this in the devers lounge, but I'm not actually entertaining the idea of making any of these hacks. But here you go:

Assasin's Creed: You could make it into a turn based RPG with Dragon Warrior. It would be a text and graphic hack basically. You'd Damascus and Jerusalem right there.

Resistance: Fall of Man: I think the best candidate for this would be Contra.

Halo: I'm thinking something Alien 3. I'm sure there's a more worthy candidate, but this reminded me of Alien 3: http://www.youtube.com/watch?v=Tbw17sLiWN4 Metroid would my other choice, probably my first actually.

God of War: Maybe Castlevania?

Super Smash Bothers: It would be neat if some of the spites were eith changed or new characters were added. I also think they look a little weird. Mario doesn't really look like himself in that.

Anybody have others or ones they think should be different?

You may be interested in a homebrew project turning Grand Theft Auto into a NES game:

grandtheftendo.com

*Actually, I just checked that out and it looks quasi-down.  Here's a thread on another forum discussing it.

Yeah, we were discussing that in the dever's forum. I hope it's still intended to be finished :'(

Oh man, me too, it would be a shame if the project just got dropped!

I've always wondered how easy it would be to hack Maniac Mansion into one of the other Lucasarts adventure games.  I keep reading that they used a modified version of Scumm 1.5 so I think you could do Zak McKracken.  

Also, King's quest V was pretty good and could have been hacked into VI or even IV.  I'd love Black Cauldron on the NES as that's one of my first games.  

What really needs to happen is for someone to come up with a NES Mouse, that would be great for all the Kemco games and Princess Tomato.

Found a topic almost just like this one here:

http://nesdev.parodius.com/bbs/viewtopic.php?t=1582&highlight=mansion