Well, I don't think the perfect game exists really. Everyone has their own tastes, some like shooters, some like fighters, some like platforming, etc.. I even like a wide variety and dislike a good variety too.
Buuuuuuuuuuut.... I do has a lot of ideas for game I would enjoy that I think others might too.
One idea was a combo of a real time strategy game and a first person shooter.
In rts's you tell your forces where to go, build up defense and attack units, etc. etc..
In fps's you run around and shoot people with guns and such and often try to meet certain objectives and some have lots of interesting weapons.
This idea was inspired by killzone 3, starcraft, mag [lots of inspiration here], metroid series [2d or 3d], 2d airplane shooters, Resistance, boarderlands, metal gear series, front mission series, and fighting games.
It would be two games. One is an FPS and the other is a RTS.
In the FPS the story mode would go alongside the online mode. In the game you start off as a mercenary for hire who works free lance. As the story progresses you start to see the different factions of mercenary groups and learn what kind of weapons they use and can pick which group you want to join. The factions are located in different part of this world and cause of this tend to work more jobs that're close to their base of operations.
The story would mainly consist of you getting the general idea of what each group is trying to achieve and what the countries they usually work for are aiming for.
Game play is that it's an FPS. The key point is the weapons and upgrades [which are inspired a lot by metroid, 2D airplane shooters, Killzone 3, Metal gear, front mission, and fighting games]. Inspired by how in front mission you start with a torso that has a maximum weight it can withstand and then you add the arms, legs, shoulder cannons, etc. on your mech. You would have a soldier who levels up in strength and endurance. The stronger he is the more he can carry. Also if he's strapped to the brim he'll move slower. You can gain abilities like unlimited sprinting, but this can't be used if you have too much weight on you.
Also you can put as many weapons as you can fit on your character. It was have a load up screen where you add straps, backpacks, etc. and place them on the body till you run out of room. I guess there would have to be set spots and you wouldn't be able to put this stuff just anywhere otherwise there might be errors in programing.
Controls would be L1 for sites, R1 shoots, L2 special abilities, R2 grenades/whatever is set for R2, D-pad switch between weapon load ups, triangle quick weapon swapping, Square reload, circle melee, X jump, R3 sprint, L3 Other special abilities. Which could be customized to whatever one would like
One of the main points is a lot of weapons to choose from. And in single player mode and also in an online mode you can unlock more weapons and receive training for them. Basically you'd collect weapons like in a metal gear and metroid game. There would also be many abilities like in KillZone3 where you can cloak, revive teammates, capture spawn points, set up turrets, and so on.
Then there's the RTS.
In the RTS single player you command a group of AI's running around a map shooting each other. You are in charge of ammo crates, where they're deployed supplying your team with weapons giving your resources. Basically just an RTS. The story is where you're a strategist and are scouted by the factions. They place you in command of a group of soldiers. If you win enough battles you become a leader of a few people in your previous position and decide which battles are to be fought and who to have where, etc. etc..
So, online the group you command is actually from the other game. You're just trying to earn money for your group and take over territories. So, you can obtain specific maps and set up useful devices for your team so they have home field advantage. Or you can deploy to another teams maps and try to take it over and decide from which directions and such.
Of course the maps would be reused a lot, but there would be a world map that's only used once with many territories on it. And the goal is to take over the world.
So, you could be soldier or commander.