When the best players of a intergalactic war computer game are hunted down by an alien bounty hunter, the survivors must band together to fight both on earth and in the game to win a very real space war. Tag Line: a war simulation so good, it's real…

'The last Starfighter' was really in a coming of age in space.
This one is really a good comedy on earth.
I am trying to write for gamers what Galaxy Quest is for Sci-Fi Tv addicts.

Too similar to 'The Last Starfighter."

The difference with Ender's game is that everybody around them knows the truth.
In this nobody knows anything except the game manufacturers who are alien in disguised.
Most of the best players of the game are kids, social misfits.
It's an action comedy.
The difference between then players in real life and the characters (general, ...) they play in the game.
One of the kid has to convince his mum to drive him to the meeting point. Another one is grounded because he has taken the trash out when it was his turn to perform family chore.

The story is different... but I wouldn't use the tagline since it could also be applied to "Enders Game"

Okay - who is your protagonist, and what will be his specific goal? How do the aliens pose a threat to humans?

You can drop the tagline from this.