As the title suggests, this thread is about you taking existing games today and splicing them to make the perfect game.  It doesn't matter if they cross genres (First Person Shooters, RPGs, Racers, Action/Adventure), all that matters is you choose elements from any game and splice them with another game to create a superior Hybrid.

As an example:

Assassin's Creed

(Free roaming, Crowd mechanics, mini-missions to collect information)

+

Shadow of the Colossus

(Massive World, Epic Boss Battles)

A combination of the climbing mechanics in both games would be suitable.

I'm sure you can think of some pretty sick combinations. Have a go. 

(Pics not needed, but they always make things look nice) 

Ace Combat 6 and Jak 3. Lovely visuals, flying parts, driving parts, platforming parts, gliding parts, shooting parts, a giant boss with a scandinavian name, a few superweapons, but best of all, only the one stealth mission with a radar net (I'm guessing this is in AC 6)

Unreal Tournament 3 + GTA + Final Fantasy/Golden Sun + some random poker game = godlike

Animal Crossing/Harvest Moon/My Sims + World of Warcraft/Everquest 2 ...

If you combined a lot of the elements of these games you could end up with a true "define how you play" massively multiplayer online RPG.

wiisports and goldeneye

Mario + FPS

Hes done good on other types of games, why not FPS?

Gran Turismo 5 + Championship Bass Fishing = Super fun racing fishing times!!!

Wii Sports

(controls minus the boxing controls cause they are horrid)

+

Graphics of
(Ready to Rumble, Virtua Tennis, High Velocity Bowling, MLB 2K7, Tiger Woods Golf 08)

Gran Turismo 5 + Killzone 2. It would basically be like a GTA game but with realistic cars and FPS.

I want a Mario game with the intensity of Trauma Center