Well, since the question was whether Rome 2 is worth buying and not whether Rome 2 is better than Rome 1 or M2TW, yes, it is indeed worth buying. If you are interested in the time period, if you are interested in better graphics (we are talking about the vanilla game and not about mods) and a more modern approach in terms of UI , music, etc then yes, absolutely, I can only recommend Rome 2.
Also you will need the base game if you want to download and play any of the great mods currently available for the R2. I would recommend one of the most appreciated and played mods for Rome 2: Divide et Impera (DeI). Used to play it a lot. That alone makes the base game worth buying, not to mention that even without mods the game runs fine and is much better than at release.