basicly write down anything you want in Far Cry 2.
1. Weapon customization,Silencers, Scope...
2. More complex Hand-to-hand combat or CQC, something like riddick the game which had blocking,counters,pushing etc... variety in fighting style too.
3. More intense Knife combat,stealth kills, more gorey animation and knife tricks etc.
4. More various vehicles like Tank if avaiable

, ATV, motorcycles... etc
6.More Weapons MP7,AKS-74U, Dragunov...
7. Great animations for gameplay such as reloading, looking down into sights, switching guns, throwing gernades, fighting etc...
8. Complex and smart AI.