You can certainly play it with 2 (one GM and one player. Some of the character abilities work better if you have multiple PCs, but there are no real problems with having just 1!
If you only have 1 player, I would recommend making sure they know about the Hirelings section (so that they have some extra muscle on their adventures), or allowing them to play 2 PCs. It's also totally fine for them to just have 1 PC, the game will just be a bit harder for them.