I play solo and I would say it's worth it, there's plenty to do as you progress through the material/tech 'tree'.
There are small dungeons scattered around that you can just pop in. It's not WoW, the dungeons aren't MP instances.
MP is just playing the game with other people for the most part, there isn't anything special added on, so it's mostly coop. You can search and join randos servers, or set one up yourself.