When StarCraft II is released, it will have been over a decade since a game bearing its brand hit retail shelves, and if Diablo III doesn't ship in 2010 -- which is likely -- it will share that distinction.

Developer Blizzard Entertainment is known for its relentlessly iterative process, which is what leads to the infamous "when it's done" release mentality, and Diablo III is no exception. Thought to have gone through several complete reboots since the closure of original series developer Blizzard North in 2005, the game has already seen significantly redesigned elements since its formal unveiling last June.

To get a sense of how that design process works -- and when the team knows it's actually done -- Gamasutra sat down with two Diablo development leads: lead technical artist Julian Love, a Blizzard North veteran, and lead content designer Kevin Martens, who spent nearly a decade at BioWare before coming to Blizzard.

The pair discussed Blizzard design and art philosophy, the evolution of the Blizzard North style, the action RPG genre, and Blizzard's flat development structure.

Diablo III was announced last year; it's been playable twice at Blizzcon now. Mike Morhaime suggested it probably won't be out until 2011. Does it feel like the development time has been extended to a surprising degree? Do you ever think, "Oh God, this really will be a while longer now?"

Kevin Martens: Here's the secret to Blizzard games, and this is a secret that won't help any of our competitors: endless iteration. We'll take something, we'll put it in the game. Maybe we'll like it when we put it in, maybe we won't. We'll leave it in there for a while, we'll let it percolate. We'll play it and play it and play it, and then we'll come back. We might throw it all out, or we'll throw half of that out and redo it.

It can be a long time, but it is fun to work on as well. That's the thing that keeps you going. Multiplayer always works, and the builds are always playable. We've played them constantly, and it's fun. You actually look forward to the weekly play session even though the game is still in progress. That's what keeps us going, and that's also why it takes so long. We'll do it over and over again until it's just right.

With Diablo, and StarCraft moreso, it will have been a decade since there's been a game in the series out. Blizzard North as an entity no longer exists. How do you determine what needs to be retained from something a decade old, and what needs to be modernized?

Julian Love: Well, as an ex-Blizzard North employee, I never got the sense that we were a standalone entity. We were always in contact with Blizzard South folks. They were always coming up. I think I saw it as we were one big company.

That said, [as far as] the real question in terms of how much we're going to take forward, we want to bring back all of the stuff that was great, that was fun. We certainly want to tap into what was great in the first two games and make sure all of that stuff is coming back, and pile in all the cool stuff we can to bring it over the top and make it the definitive version of the series.

On the topic of Blizzard North and Blizzard Entertainment though, I do feel there was a difference in style between the Blizzard North and South games. The Diablo titles had a more baroque, intricate look, more tilework and stonework "along the grid." Diablo III is more of a blend of that style with the current Blizzard South style. How long did it take you to settle on the look for Diablo III?

Julian Love: Well, it took a while for us to settle on the actual style, but I don't think it was due any kind of difference between Blizzard North and Blizzard South philosophy. It had more to do with the fact that we were moving the game from a two-dimensional technology platform to a three-dimensional technology platform.

Issues like lighting and separation between the characters and the backgrounds are handled in entirely different ways -- ironing out how to get what we felt was a Diablo vibe while still managing to get the characters to pop.

Looking at D2, for instance, those characters are super bright, super colorful. They pop out of the backgrounds. So, we had to try to bring that forward, but at the same time we don't want to just rest on that art style and do the exact same game.

We want to elevate that. We've got to look at the other games that Blizzard does, learn from the things that they've done that make those games better, and really progress. I think what you're seeing in the art style is our idea of the actual progression of the Diablo universe.