The single-player demo gives you some nice glimpses of the plot, the squad based action, and in my opinion some of the nicest graphics seen in a sandbox on the 360. This is particularly true because I was playing on my standard definition tube, and still felt like the scenery was mostly lush, even up close. I noticed some issues with the destructible world elements graphically in solo mode but overall came away impressed.
Where this game shines (like all the prior Battlefield games) is in multiplayer mode. Not to ruin too much of the plot, but your squad this time isn't driven simply by patriotism. It seems the fellows of Bad Company have a bit of Jack Sparrow in them, and are equally motivated by the prospect of gold bars. In the multiplayer demo, you play on a level called "Oasis", which has several small villages laid out across the map. Mountains and water make up the left and right of the terrain, giving a good indication of the types of play available in the various levels of the final game.
Combat is sharp and balanced, and even a mostly below average combat/action player was able to move up a few ranks after only a couple hours of time. If I have any gripes at all, its that the helicopter will need to be "nerfed" slightly, because right now a helicopter pilot who knows what he's doing completely takes over the game. Perhaps with some of the unlockable demolitions weaponry it will be easier to counteract this, but as it stands, tanks and AA guns are little trouble for the choppers.
One last interesting item of note is that progression through the ranks in the demo earns you unlockable item that can be used throughout the real game. I won't give away what it is, but if you plan to play the game regularly, it's probably worth your time to get into the demo.