The Binding of Isaac is "closing in" on 450,000 copies sold, and such success has surprised creator Edmund McMillen, as he had convinced himself this "week-long project" would garner little interest from the public.
Speaking in an interview with IndieGames, McMillen said there was "no reason for this game to have done well," because when he started the game, he wasn't sure if he should even charge for it.
"I didn't think people would want it, in all honestly," he said. "I had to shop it around to a bunch of different developers, and say like 'Do you think I could sell this?', because I thought it was way too weird, I thought the content was too disturbing and creepy, I thought it would just rub too many people the wrong way, and I thought the design was just too hardcore for any kind of mass amount of people to enjoy.
"Permadeath is very discouraging, that's why roguelikes are very niche and small. There's very specific people who play them. There's another key thing too, what traditional roguelikes, that use permadeath like that - most of those are free. I came to the conclusion that I'd put it up for $5, and if people don't like it they don't have to buy it. Then it just f**king blew up. I didn't know, I didn't expect it."
McMillen said the popularity of Super Meat Boy "helped" sales of Isaac, which has also led him feeling a bit guilty Team Meat's programmer Tommy Refenes wasn't involved.
"I wanted to do this with Tommy, I don't want to say that to sound bad to Florian [Himsl], but this was a game I wanted to do with Tommy, and he just wasn't available when it was happening," McMillen explained. "It was supposed to just be a week long game jam, I wanted to jam out this little idea I had, just to have fun, and it just kind of grew and grew."
The game's growth will continue with the release of The Wrath of the Lamb which McMillen likened to "the final ultimate chapter in the game." According to him, the expansion will contain an alternate, much more difficult chapter to Sheol which will be the "true final ending."
"You'll be rewarded by beating that part of the game with each character with items that are really unique," he said. "There's a lot of really unique items, new items sets, even new player statistics. There's a speed of shot stat, not just rate of fire, that can actually be modified now, which is cool to mess around with. There's also a bunch of new tear types that goes with the items.
"There'll be definitely a lot of interesting things that appear as you play, maybe even more if I feel inspired."
Continuing on the subject of Isaac's growth, McMillen said a 3DS version of the game is still "up in the air" at present, and while he couldn't discuss details regarding it, talks regarding the handheld version are "quite in depth to the point that it's taken this long for a conclusion to be met."
"The game has definitely thrown a wrench into the gears of the people involved," he said. "A lot of people don't know, even I don't know, exactly how to take the game."