It says the game's for from 2 to 6 players, but how does it play with different numbers of players? Is there a "best player number"? Is there one that's particularly bad?

4 is our usual number - the game works perfectly. It sure can handle more, but in that case I would go for other games.

How about fewer players? How does it play with only 2 or 3?

2 players are not enough - too little interaction. 3 is ok, but as I said above, IMHO 4 is the number.

We've played with 6 and it's great. It gets more difficult to decide whether or not to pass out of a battle with that many people. It is also more of a challenge to win as there is much negotiation when the territories are mostly claimed.

I found that more players require different planning because there are more opportunities for them to play a card that can completely screw you over (especially the surrender card).