Command & Conquer 4's two campaigns can be played single-player or with friends. If you decide to go it alone, though, you'll still need an Internet connection.

Here's the explanation from an EA community manager:

As of right now, you need to be online all the time to play C&C 4. This is primarily due to our "player progression" feature so everything can be tracked. C&C 4 is not an MMO in the sense of World of Warcraft, but conceptually it has similar principles for being online all the time. While some may be taken aback by this, we've been testing this feature internally with all of our world-wide markets. We wanted to make sure it wouldn't take away any significant market or territory from playing the game. We have not found or seen any results that have made us think otherwise. You won't need a fast connection, in fact, you could be on age-old dial-up, and have the same single player experience as everyone else. Online all the time won't cause lag for single-player. We've also heavily worked on the online infrastructure such that people with slower connections will not lag other players with faster connections in Multiplayer.

The game appears to have an RPG-like element to it where you grow in power by completing battles. Requiring players to play single-player campaigns with an Internet connection seems like an effort to ensure that they'll be adequately progressed when they decide to move on to multiplayer. It sounds logical but the anti-DRM crowd is probably going to think this is just stealth copy protection and tank the game's Amazon.com rating.