Gameplay and story are both important. Sometimes an interesting story element can create an innovative gameplay feature. Usually, people come up with an idea, which turns into a game, rather than looking for an idea while making a game. That's why if anybody has an idea for a game please post it here…
We can discuss gameplay, but in this thread, it's all about the story.
Yeah, we've gone through 2 pages and not had a single idea yet. I was thinking of a story like Starcraft.
Story is the most difficult part. It's like with the design of software, errors in design are hard to fix. The same is true for the story of a game, if there are errors, its hard to fix afterwards, without introducing some deus ex machina 
I'll come up with a story idea in the next few days. Promised.
Inspiration material…
Made for 2.5D shooter.
Introduction
There are several planets in the outer regions of an intergalactic planet confederation. Those planets are populated by humans and other life-forms. The humans came here a long time ago. In most cases, they don't even know, that they are part of larger system of planets. This information was lost somewhere in their history.
The planetary outskirts are very interesting for the rivaling factions of the galaxy, because there are a lot of resources, the inhabitants don't care about. And most inhabitants are no threat for the technological superior intruders.
But there is one faction in the universe, that tries to bring some peace and order to all the planets that belong to their confederation. And there is one important opponent to this confederation. Those two factions are in a constant cold war. The first faction is called the confederation, and the second faction calls themselves the free.
The two factions are not bad or good, they just follow different goals. And every faction needs resources from those outskirt planets, so they try to exploit them. On the other side, they are constantly trying to weaken their opponent. If they find some planet, where the others have already installed some extraction facilities, they don't attack those facilities directly, because this would turn the cold war into a hot war, and nobody is up to risking this.
So they let others fight on their behalf. They support the inhabitants of the planet to fight the intruders, by providing weapons, technology and information (mostly propaganda).
But the others do just the same. This way, a war breaks out on the planet, between the inhabitants, supported by the two factions.
The story of our hero starts on such a planet. The war was going on since years. Nobody remembers when it began. On this planet, technological development is at a very early stage. The first habitants came to this planet, because they were thrown out by the confederation. And they were only left with minimal technology, so they could survive, but never escape that planet.
The planet isn't fully explored yet, only a small part of the northern hemisphere is inhabited. The extraction facility of the free is installed in a region, the inhabitants never have entered before. But the confederation has infiltrated some people, to explore this region of their planet. To avoid, that this might lead to some production problems in the facility, the free are trying to keep the people away from this region, by helping some villages to defeat those explorers.
This is all possible, because the people of Hills (the name of this planet, named after its first explorer, Geoffrey Hills) fell behind to some ancient behaviour, where they believed in some gods and magical powers.
The free told their supporters, that those foreign explorers try to find god in that region. And if they would succeed, god would become very angry about that.
The confederation on the other side, promised, that in this region they would find immense riches and maybe some answers to some old questions.
Who or what will the player be
The player will be an individual, living in one of the villages of this planet. he has to decide, which one to support.
Goals
Villages are attacked all the time. So at first, the villages have to be defended. In later stages, villages of the other side have to be attacked. There is the possibility of single person missions and others (exploring some region, fighting new life-forms, developing/stealing technology, escaping the planet, find new planets, do some trading, etc., etc.)
As a codename for this story i would call it: Proxy wars
I approve this story. Very good.
About single person missions, an example: the village needs food, and you go to the forest to find food, the food is hidden in somewhere and you have to run and jump in the forest, when you find the food there is a enemy next to the food and you have to fight.
It's a mix game. it's not a Rts game, FPS , run and jump. It's something better, some new. It's a mix.
It's the game of the future.
Next to the hill planet there is the Monkey Planet. hehe
A good name to the hero is Fabio. 
Thanks.
The main aspect of this story is, that it can be extended in any direction. We can introduce dangerous aliens, or we can create a planet, where swords are the most modern weapons. Based on this story, even a MMOG scenario is possible, with PvP and PvE. Any genre is thinkable.
Story:
Strange accidents occurred, people disappear , a fanatic organisation assassinate politicans and nobody knows what's going on. Except of you!
After returning home, you find your family dead, their bodies are ugly blemished and you can only think "Why?".
Nobody believes you, that you are innocent, so they judge you guilty.
There is only one place for insane people, lunatic asylum in other words hell. Trapped like a rat, with no way out, you start to believe what they tell you.
Your would have lost your mind, if you haven't met this strange young girl. She killed three people on the street by daylight, without even carring for witnesses or trying to run away. She were standing there, her coat stained with blood and was laughing. And this girl is telling you that you are innocent and if you want revenge.
Why not? You didn't take her serious, there is no way out! Your first mistake!
This evening a group of four people is inflitrating the lunatic asylum and free the girl. And you!
"I keep promise! Will you?"
The guardians have no chance against the heavy armed soldiers in strange armors.
Your way leads to the roof top where something grasp your breath! A spaceship, which pick you and the other up…
Your journey begins, a bloody path and you will soon realice, that hell is a dark place without light. You are surrounded by enemies, you can't understand. You hunt them, they hunt you and suddenly it doesn't matter if human or not, you pull the trigger to survive!
Background:
You are part of the fanatics or first it's seems like that. In fact, they are a organisation, which hunt any treat to earth. It doesn't matter if monster or human, you must obey them, or they kill you. Everyone is nice to you, but you and the others a mere tools and you start asking questions.
Who are they?
Who are the others?
Who is behind this?
Who has killed my family?
Who is this young girl, that seems to know everything?
WHO AM I?
You must decide, which path you take and it will decide, how it will end for you!
Enemies:
Your enemy has many shapes. You don't know, where they are comming, nor why they are here, but one thing is sure. The are aliens, strange creatures with dangerous abilities. Some can take the shape of a human, some can controll the minds of humans and other are so strong to throw a car in your direction. You must find their weakpoints and kill them. Therefore you has access to different weapons, common rifles or alien weapons, but strength is not the path to victory. You will have to use your brain to survive this story, or at least not to die without knowing the truth.
Gameplay:
Before every mission you can choose your weapons and your team members. Every team member is different and they can die. As an team you have to find the aliens and kill them. Sounds like an easy plan, but when is everything going like plan. Sometimes the tables turn and then you are the one, who is running for his little life!
The good thing on this story is, we can include space material and normal material, the main character can travel to space or he never leaves earth. Maybe you are on the wrong side? Add your own ideas!
Ok good story, but the gameplay need be more flexible, remember It's not a FPS it's a mix of styles. You need strategy elements and a world to be explored. Think about.
I am afraid of this girl, is she single?
Frightining story. Can you give it a code name?
I will summarize the story ideas in my first post for easy navigation.
Yeah and she killed her own family.
That's why she want to help you!
So a good code name would be: Lunatic serial killers?
I like it and can go on it, but could you fix your grammer or have someone fix it for you? I am having trouble reading it.
Varamir: Just saw your story and am reading it.
Ok, I vote Vardamir's story, but I am fine if we go with either one, as they are both good.
Codename: Project Zero
Just kidding. The story was originally invented for Project Zero, but the concept was to complex for one person to create, so in the end I chose a simpler story.
I would like the codename: Paranoia
And I 'm sorry for the bad grammer. I was in a hurry!
I will fix it and somewhere I have the extended story(german), then I can give you the different characters, weapons, etc.
I have renamed your idea.
I can add a column with votes to the table in my first post.
Darkphoenix's idea about having mortal party members with special abilities kind of reminds me of both The Thing (crappy game) and the Rainbow Six games.
I want to stay away from a pure FPS, because there are gajillions of FPS engines already out there. You guys think we could combine FPS+RPG+RTS with one of these stories?
Not FPS, FPS/RTS is what has most likely been decided.