Thus the hallmark of IGI - vast, open, terrain. All that real-estate makes for some very interesting level design. The developers are working on massive levels that take full advantage of the engine. The demo mission should give you an idea of just what the engine is capable of, and the final rendering will be D3D accelerated. The physics model beneath the game is just as interesting as the game's engine.
Bullets have real trajectories, with both wind and material affecting a bullet's path.
If an object is thin enough a bullet will pass through it. This is very cool indeed. Play the demo and discover the joys of physics. IGI is strange in the sound department. A game that stresses on stealth should present you with audio clues.