Online's much better than the single player story. It's got the usual PvP stuff like 6vs6, domination, solo and 3v3, but you can also do Strikes, which are like a single player mission ramped up in difficulty, and for up to 3 players so it encourages co-op. If you just want to go small missions yourself you can go on a 'patrol' of the world you're in and then you get a random public event happening whereby whoever is around you can help you fight a timed enemy. And when you get a high enough level, you can do Raids which are for 6 people and are meant to be bastard-hard, however you can only do that with people in your friends list.