Deffinatly needs an engine like F.E.A.R., maybe a GeoMod like from Red Faction.
As for gameplay, Id like to see some new abilitys for the pred. Preds need to be able to run and jump faster and higher than humans,, by a lot. Maybe a limited climbing ablility, moving around rooftops rather than in halls like [most] of AvP2.
The aliens, Id like to see acid spit incorperated somehow. Like able to use once after building it up, and it takes so long that maybe once or twice each level it can be used.