When you're looking at the board by yourself, you just concentrate the terraforming part of the game, ignoring actions that give you victory points. When you have other players to think about, it requires a lot of consideration about scoring--or denying your opponents an opporunity to score.
This time, my two opponents seemed to get their economic engines running long before I did, and I thought I would finish a distant third. However, after the planet was terraformed and we tallied up the points, I came in first. But even if I had come in last, I still would have enjoyed playing. That's because Terraforming Mars is a fun and challenging game that gives me a different experience every time I play. If you're into boardgames as well as wargames, you should give TM a shot.