Here we go again... Sorry, it's just you are not the first person to ask this question.
Basically, you'll get different answers. Personally, I would say yes. I think Rising Tide adds a lot to the game. It adds interesting new sponsors and new mechanics that add to the gameplay. Artifacts, water cities, hybrid units, the new diplo traits and the ability to buy/sell resources through espionage are great. If you enjoyed base BE, you should definitely get Rising Tide.
Others on this forum will disagree with what I just said. There are many who feel Rising Tide does not fix pre-existing problems with the game and does not go far enough. Some also feel that the game is simply not challenging due to the poor AI.