IGN had a chance to play with the Command & Conquer 3 Demo. Here's a snip from their writeup:
Next week Electronic Arts will be debuting their newest addition to the Command & Conquer franchise to the public when they release their first single-player demo on Fileplanet. The exact day is, as of right now, not perfectly settled, but it will be next week. Could be Monday. Could be Friday. Either way you can start your anticipation engines. Lucky for us, EA agreed to let us have a go at an early build of the final demo to get a look at what will be included. We've had the chance to play it, take some screens, and enjoy the explosions.