The RWS and the Thoth have a lot in common. They are both based on the Golden Dawn deck, so share a similar structure and history. RWS however was intended for public consumption and the Golden Dawn deck at that time was a secret deck, so a lot of the similarities have been obscured.
The Thoth blabbed all the secrets, and also changed the deck significantly to fit in with the philosophy of Thelema and its mythology.
The cards are quite similar in a lot of ways and share a lot of meanings. But there are also areas where they are quite different to each other. e.g. in the Thoth the Hanged Man is a more negative card than the RWS, because the idea of self sacrifice is contrary to the ideas of Thelema, but complimentary to the more Christian RWS. The World card and the Hanged Man are quite similar in a lot of ways, but also there are differences that might affect a reading. Judgement and Aeon are very different, though may mean the same thing in a reading sometimes. It depends how you read them I guess.
You can learn more about each deck by comparing them to each other. Its a good way to study the difference I think