A lot of his old stuff (the archive) he has for sale. His current / new series that he does are all free.

So if you want to see if it's your thing, try out Supernova in the East as it's still on the free tier.

His paid stuff is definitely worth it, specifically the other series that the other reply said. It's honestly a great deal for the amount of content you get per episode.

Prophets of Doom is his standalone masterpiece; Death Throes of the Republic and Wrath of the Khans are great starter series. Everything after Ep. 30 or so is generally pretty solid.