The game was originally released on the Kindle as a kind of experiment to see if you could make a game on there. (you can, although there are some pretty extreme graphical limitations) The Facebook iteration is pretty nifty. The presentation is excellent and fun, but it's really the game mechanics that do it for me.
You match 3 objects just like any other game of this kind, although instead of moving objects on the board, you can only place new objects. Instead of things disappearing after a match, the objects merge into a single, new, upgraded object, kinda like how in Hexic you can create new pieces by forming certain configurations of jewels. Except in this case, you're tending to a garden, which you slowly build into a village, then a town and eventually a city.
Since your ability to change things after you place a piece are pretty limited, very careful planning and strategy is required to succeed at Triple Town. It's a very different game experience, you're kind of "cultivating" or "growing and grooming" something in Triple Town, where as in games like Bejewelled, Puzzle Quest, etc. you're just trying to combo stuff up and "destroy" jewels or your opponent.
It's a very chilled out experience, but be careful though, it can really suck in your time!
The game is in beta right now, but it's very playable. Get at it!