Well, don't buy it without really looking into it.
I buy board games. Lots of board games. I listen to board game podcasts. I got to board game conventions. I love board games.
I won't buy a game unless it has good:
Art
Components
Theme
Rule Book
Mechanics
Packaging
And there are way too many great board games that have all of those, to bother with games that don't.
And Terraforming Mars has horrible components. And horrible art.
The game is great - I love the theme, but the artwork on the cards is just horrible. Some look like photos. Some look like paintings. Some look like cartoons. Your player boards is just a flimsy thing that you keep track of like 6 different things on, using cubes. If you bump your board, even slightly, the cubes shift and it's a pain.

But like somebody else said, they came out with Terraforming Mars: Ares Expedition, and the art and components are so much better. The player boards are double-layered, so the cubes stay in their little square, even if you bump them. The artwork is all uniform. The gameplay a cross between Terraforming Mars and Roll for the Galaxy (a game that I love), so I almost never play either of those anymore, and just play Ares Expedition.

But, maybe you found a deal on Terraforming Mars, or you're just not that concerned with every aspect of the game. If you can look past it's short-comings, it's a great game - great theme and mechanics. I'd just rather play Ares Expedition.