I dreamed that a hundred people were confused about my last post, so now I feel compelled to post about the nature of themes.
A theme is not a plot. It's a kind of underlying concept that you explore.
This is not hindsight or bullshit deconstruction: many of the best works of art in every media have a consciously chosen theme.
For example, Shrek. The first movie had the theme "self confidence". Virtually every character was defined by their self confidence and the measures they took to protect it. This isn't me plucking the idea out of thin air: I read it from an interview with the writer. He consciously focused on the idea. And the first movie was great.
The thing is that the same characters in the same situations with no theme wouldn't have been nearly as tight. The sequels attest to this: they had much weaker themes that weren't really very compatible with the design of the IP. In turn, they weren't as good.
I think that the audience (or players) understand the nature of the theme at some level, even if they can't put words on it. There's just something that "clicks" when everything is exploring a specific theme. Donkey and Shrek just "click", even though there's no particular reason they should: they click because they're both exploring self-confidence from different angles.
As a game example, I think that the Star Wars universe is at it's best when exploring the theme "power corrupts". This sounds like a dismally dark theme, but that's not really the case: the struggle to resist the corruption is a big and rather shiny part of the universe.
There are a million ways to resist it: make oaths, join a brotherhood, fall in love, find a friend, etc, etc, etc. No matter what the path, corruption still drags at you, and that can be very interesting to see what sacrifices arise.
It's also interesting to come at it from the other side: if power corrupts, what does lack of power do? How about someone who is only powerful in a specific situation? How about different kinds of power?
That's just the light half. The dark half is also fun, exploring the millions of ways to fall and the millions of types of corruption...
It would seem to be primarily a story theme, wouldn't it? I mean, can the rules of a game actually contribute to this theme?
Throw away your d20s. There are any number of rule sets that give enticing, corruptive influence over the player. A time-honored tradition is to statistically reward the player for doing dark deeds. My personal take on the matter is much more complex: I built and refined a very unique system that seems to do the job very well. The rules of the game revolve around the idea that power corrupts.
In fact, I think it makes a stronger case. If you just see it, you get a lot of people who say, "well, I wouldn't fall..." But if you live it...
I think this makes the game a much stronger, tighter experience. Sort of like in Eternal Darkness, where a primary theme was "madness". While the examples of madness varied hugely, they all "fit together" because they were all pursuing the same theme, just from various directions. It's a simple, clear example of what I'm talking about.
I hope this is clear...