Legacy model packs: The ability to use all the models / weapons / characters of the first FPS Creator's Models Packs.
Choosing the size of the map: From very small to very large, even infinite.
Destructible terrain and buildings: Building destruction like Red Faction Guerilla or Battlefield. Terrain destruction/mining like Voxel based games.
In-game construction system: the ability to use in game the construction kit, so the players can construct their own buildings if they have gathered some ressources.
RPG system: Create npc's, quests, rewards, dialogue with multiple choices.. The basics to re-create a Skyrim-like game. Why not an intuitive and easy-to-use system like RPG Maker ?
Simple 3D Model Creator / Editor: so we can easily create simple assets.
Block programming: Similar to the software Flowcode, so users don't need any programming knowledge to create their scripts.
Vehicles: adding vehicles with a destruction system like GTA. Why not a feature to easily create our own vehicles, and why not a feature to let the player create his own vehicle in-game ?
Weapon creator: a simple system to create our own weapons. We could assemble differents parts on a rifle, on a gun or on a melee weapon, and define it's characteristics. Possibilities are endless.. And why not a feature to let the player create his own weapon in game ?
Realistic dismemberment and blood system: A zombie game without gore is not a zombie game. And a game is much funnier with gore !
With this features, GameGuru may be the best and easiest Game Creator ever created, with lots of freedom offered to users.