Playing through the single player story is absolutely fantastic, and you can play through it with friends at any time, if you want to change it up, everything is multiplayer as well, it's great! The levels in the game get continually more and more complex, all while the game play is incredibly simple, and fun.
The game includes a Level Creator, you can publish your created levels up into a online lobby with-in the game, and make in very easy to search for other users levels and play them, either alone or with a friend. In a way this game will never run out of new content.
The DLC continues give weekly from the time it was released, and a few weeks ago a major up-date that was tied to a Metal Gear Solid pack, and comes with new levels to play through as well as new items and materials, plus some new game mechanics, you can now obtain a "gun" that splatters paint, and you can now create "bad guy" turrets that shoot at you. it's quite awesome!