I think Epics GDC talk on the improvements made to the Unreal Engine is a really good starting point if you want to know what the next Gears game will be like.
-Expect to see a revamp of the graphics, especially a new lighting system.
-Destructible environments.
-Hordes of Locust. Not 3 or 4 but hundreds as was shown at GDC.
-Greater interaction with objects, they showed off a huge cube of meat and a mercury type substance with realistic viscosity.
*and generally a "more bad ass game than the first." (CliffyB)
Obviously we don't know what the game will look like yet until E3 perhaps but i think this game will again have the WOW factor. I don't know if it will be the best looking but it will certainly be on par with the likes of Resistance 2 and Killzone 2.
