What gets YOU designing?

I don't think there is anything wrong with starting with the theme. In fact that is what I do every time. To me, designing a game is a process where I come to think that a certain thing would be interesting to do (For example: Being a general, being a national leader or whatever else you can imagine) Then once I have something I would like to play then I try to think how I want to do that.

That way I usually make mechanics that fit the theme because I only impliment them BECAUSE of said theme and not because I want that mechanic in the game.

I fear that by starting with the mechanics that the theme would end up being pasted on and just be whatever the designer could make to fit.

So in my expirience I say Theme first and once you have a theme that you really want to play then the mechanics come easily

I sometimes start with a theme, a mechanic or a desired experience/story.

I don't think there is a right or wrong way to build a game. There was a Dice Tower podcast that said the great designers start with a desired experience and create a game from their. Having never tried that approach before I gave it a go and the game created from that approach is now what i call an "active"game. (I spend money and significant time on active games to make them "pitch-able and play-testable") However, I can not be sure I would not be able to get to the same game outline is I had started with a mechanic.