BF3 will be using the Frostbite 2.0 engine. This engine is commonly thought to be the engine behind BF:BC - BF:BC2. However, DICE has made it clear that no games have ever used the technology of Frostbite 2. Frostbite 2 will probably offer the best environmental, audio, and graphical advancements in a multi-console game ever. Better yet, Battlefield 3 will be the one to lead the new engine technology. Expectations of the engine are based off of previous improvements from 1.0 - 1.5, expect better sound, better physics, a more destructable environment, improved textures, and real-time weather changing.
Battlefield 3 is expected to be set in the modern warfare era. Expected factions include the US military, Middle Eastern Coalition, China, and/or Russia. The maps are expected to be larger than BC2 maps with more vehicles and game play improvements over past Battlefields.