You can follow the story-lines, one or many, in whatever order you choose. The game really is completely different depending on how you build up your character. The expanse of it is truly amazing. Or, you can just wander around, check things out, till you wander too far and get mauled by something way too powerful for someone who's just wandering around in the wasteland. The depth of the crafting/building system alone is mind-boggling. Go to youtube and see some of the videos of buildings that people have created. Just amazing. Many, many hours of discovery and playtime. You can keep going till you become so bad that you can do anything and go anywhere, or you get bored of doing ALL the missions (there are a TON) and just turn on god-mode so you can see everything.