If you have enough optional ways to victory instead of the most powerful and the ability to get to those options before a steamroller player can roller over everyone then you have a very challenging game to the end. Let players turtle and let them steamroll, but, have those avenues that other players can do that beats both of those types of players in their wakes and makes them cry and cry and cry foul foul foul. lol One thing I enjoyed in GC2 was as I was playing steamroller I got beat by influence power. I never even noticed it, didn't even care about it as all games before had always been beaten by the steamroller effect alone. So, I can't emphasis enough adding many ways to win and ways that can sneak up on a turtler or steamroller and really surprise the hell out of them for not paying attention to the whole game instead of just their own agenda for winning.
The real world corollary to this analog.
If anyone has watched the show Survivor. There was a player Russell, during the last 2 seasons. In both cases he played the role of a villain to the hilt, and in both games, he got to the final Tribal Council. And while there, from his final tribal votes, he never got a single vote.
Jeff Probst asked him this last season on the reunion show, did he not understand that he was missing out on the social aspect of the game. And he couldn't comprehend that. He could only ever see it as playing the game the best way to get to the tribal council. And from there he thought that everyone would vote for him for being the best player up to that point.
He couldn't fathom, the reason why no one would vote for him. And that's because on his way to ensure he got to the final tribal council, he burned every single bridge, and strutted his feathers like the big bird he thought he was.
Colby described the situation best as, Russell played the game to get to the Tribal Council. That was the game HE was playing. And while he may want it to be voted on by America, for who's the best. (And Jeff Probst continued this train of thought.) That ultimately it's the game of Survivor and that's voted on at the end by the Survivor's themselves. That's the rules.
I have sympathy for Russell, he did play an awesome gamestyle right up to the end. But he just couldn't comprehend how the enemy beat him. In the end it was women who he saw as less a threat, that ultimately who won from under his feet.
So all things being considered, I'm looking forward to games like this where there are steam rollers, and turtles, and smarmy diplomats, who intermarry the entire continent to their family. And then the spell researchers are making their headway towards the ultimate spell, and the final ultimate adventurer finishes his quest. All are viable, and will really challenge the player. Sounds like fun to me... so that way folks just don't assume they win at a certain point.