Designing a successful casual game is a matter of balance and precision, and Bejeweled, Zuma and Bookworm creators PopCap are one of the masters of the art, with a projected $170 million in sales in 2008.

So how do they do it? The company has just released Bejeweled Twist, the first major gameplay update to its popular match-three title, and one that significantly changes the way the game is played. 

So on the heels of the game's release, Gamasutra spoke to co-founder and chief creative officer Jason Kapalka about just what separates a "clone" from a true innovation in casual gaming, and how he balances his games to be accessible for his core audience.

Of particular interest is Kapalka's assertion that -- legal issues aside -- there is a "moral/ethical" question about what constitutes originality in the casual space; he also views the creativity issue to be one hardly relegated to that space -- "You can't imagine how World of Warcraft could have existed without EverQuest."

Let's talk about design for Bejeweled Twist. The core mechanic reminds me very much of one of the modes in Super Puzzle Fighter for Dreamcast. Have you played that?

Jason Kapalka: I've played Puzzle Fighter.

You haven't played the mode where you rotate four blocks?

JK: I don't remember that one, no. I wouldn't be surprised... since we've started working on it I've run across a number of games that have the mechanic of rotating things.

In a sense it's like Hexic only with, you know, a square grid rather than a hexagon shape. So I haven't played that one but I'm not surprised.

You should try it. The thing I miss from playing that one when playing this one is being able to rotate the other direction. Why can't I do that?

JK: That is definitely a question that's been asked many times. We certainly tried that. That's one of the first things we did, when we put the game together -- put in an option to rotate the other direction. And the truth of it is, it actually, it doesn't actually make the game better for the majority of people.

Actually, the problem is, at least in this game -- I'm not sure about the Puzzle Fighter game -- it increases the number of possible moves by a dramatic amount, so it slows down the way you play.

You suddenly have a lot more potential moves any time you scan the board, so instead of playing the game in a fast kind of way, it slows you down since you have so much more to consider. You have to consider left, right, left, right.

It's one of those things where, for the average player, it makes the game more difficult, even though it actually theoretically makes it easier, because you have to consider a lot more to play it.

It sounded like a good idea when we tried it, it's the same problem we had with some games like Bejeweled. Technically there's no reason in Bejeweled you couldn't allow people to move jewels diagonally, as well as up and down.

But it's that same problem that it increases the move space by a huge number, and suddenly, for most people, it just makes it a lot slower, and more deliberate of a game -- which for most people, is less fun.

So keeping it like this ends up making for a much faster and more immediate game. The other way becomes too strategic, and slows things down. But hey, certainly you're not the first and you won't be the last person to ask why you can't do that.

Was it turning older players off, or things like that?

JK: Well it wasn't just older players, really, it was really kind of everybody. It was one of those things that sounds like it made perfect sense to try. It was practically one of the first things we put in there.

There was one drawback which is that it would require right mouse button, and that's often a problem, and that is a little bit of an issue sometimes for more casual players; they just don't get that the right mouse button is there.

But really it wasn't even that, the thing was that after we actually tried it, once people started playing it, the fun factor just went down radically, something about it just became less fun. So out it went!