Cool Things: A System that allows you to make you World to a weapon! For example: put a chair in your hand and throw it after your enemy! or use a gravity gun like in HLČ episode one or a Portalgun like in HLČ-portal!
Maybe a flyindg Board like in the 1. and 3. Spiderman movie would be cool!
Tuneable Weapons (Ammotype-Change,silencer)
a full destroyable World(Terraindeformations,destroyable buildings)
And my faforite feature in MY Game: a 2 Player-mode!
Btw you make EXACTLY the same Game, like me! ^^ But my Game is fully in 1st person. If you want are interested you can look at my Website(in my signature)