Games are getting more and more polished, and developers are way more worried about getting people to the end safely, and entertained. I ask because I know you like classic games: do you ever worry that the corners are being sanded off a little too much in contemporary games?

DM: Well, that's a tough one.

If a game becomes an escalator -- like you just have to ride it to the end.

DM: Exactly. You don't want that. If your difficulty is just kind of like this the whole time [Mustard traces a long, flat line with his hand] then probably, it won't be fun. It will get boring way faster. I'm not saying in all cases, but I think in many cases, it will get boring. The moment-to-moment will get boring, before they get any sort of payoff from your supposed ending.

I think we inherently want to be challenged, as human beings. Inherently as human beings, we're always trying to progress. If you see a river that's flowing, we think that's beautiful. If you see a river that's totally stagnant, I guess that wouldn't even be a river. It starts to get pond scum, and bacteria, and it's stagnant and disgusting. We want to be progressing. And so I think games have to echo that.

And that's why I love games like Metroid. Because I finish the game as something different than when I started the game. My moment-to-moment gameplay has evolved, and I think that that's something that we try to imbue in our games. And that has to be imbued in the difficulty.

When we were working on Shadow Complex, Ken Lobb at Microsoft -- who worked at Nintendo for a long time, worked on the original Super Metroid -- gave us some really good advice on difficulty balancing. You want to have these spikes in difficulty, where it's ramping up in difficulty -- until they reach the point where they can have kind of this cathartic "I defeated the God King!"

And then the game does need to get easier for a while. You need to almost have it be hard, and then when they get a new weapon or something -- I don't want to give too many tricks of the trade away -- but we even went so far in Shadow Complex to do stuff where, when you beat a boss, or you got a new weapon, we actually purposely made the guys for the next few minutes weaker and easier, so that it was like, this big hard thing, and now it dips down.

And I can just get to know the weapon, or I can plow through bunch of guys and feel like I'm totally awesome, "Yeah! I beat that boss!" I'm still riding that high for a little bit. And then you kind of creep it back up to normal, and start the escalation again. And by doing that, you give people that sense of progression, and that makes for a more fun experience.

But I think on the flipside, it is still good to get people -- again, depending on the game -- but in most games, especially if it's narrative-based, you want them to also have that cathartic narrative moment as well. And so the best games are the ones that make it difficult enough, and give you those waves of difficulty that you want to keep escalating, and you want to keep progressing. And then you can also get that narrative payoff as well.

Most games -- these numbers might have changed -- but when we were really looking at these numbers, like two years ago, it's like most games have a 20 to 30 percent completion rate, of people that actually finish the game that buy it. The really good games have a 30 to 40 percent completion rate. Shadow Complex has a 70-plus percent completion rate, and Infinity Blade has an even higher completion rate.

Well, maybe Infinity Blade is because it's so much shorter, but we tried really hard to make those few times that you died at the God King to feel so brutal and so devastating that you're just like, "I've got to get that guy! I need to overcome that difficulty moment." We made sure that our biggest narrative punch happened at the same time, so that you got the emotional, "Yes, I finally did it!" and slammed that sword into that guy's chest, and then we hit you with our big narrative stinger, our big narrative twist.

There was very little narrative in Infinity Blade I, but when we did it, we did it right. So you would go "Oh... ohhh!" And I think that's a big reason why it's taken off so much, because you're already emotional about this victory you had, and then we go dun dun dun! And then they go, "Oh, I want to know more!"