I want to add about playable human characters.
Apart from nice looking models and animations, the most important moment is interraction with the environment. What do I mean? In many games, embarking and disembarking vehicles is made simplified - no process is shown and in many games you cannot act when sitting inside of vehicles of other objects.
I want playable humans to be able to, for example, jump and walk inside of transport airplane, shoot from weapons sitting in truck's back, get inside vehicles using programmed animations for each vehicle, not just teleporting to driver's position, hit objects with weapons or hands if collision detected, not just penetrating the walls. Also sitting on the armored vehicles is a great examaple of this. This thing is used in some armies of the world to make disembarking rapid, to get extra capacity or to have doubled defence and more chances to survive from mines.
People must be able to carry objects (on thei back, in hands, on their suits, or can change their uniform). Several models of different body types can be made and a lot of addtional addon objects will be weared on them... Would be nice... Also many faces can be made to choose from.
P.S. I'm for OpenGL as a crossplatform engine, it will bring people from different OSes and will make engine really universal.