One of the odd things about last month’s Mercenaries 2 was that the online co-op — while considered the most fun part of the game by the critics — was tethered. Get too far from the other player and you start taking damage. This is better than Grand Theft Auto 4, which features extremely limited online co-op in what I think is just one online mode, and even now I don’t understand why Rockstar hasn’t tried to sell me additional online co-op modes for the game. Co-op is very popular these days, just ask Nick “Bapenguin” over at Co-Optimus.com. The whole site is dedicated to it!

This week Nick has an interview with James Tsai, the lead designer of Saints Row 2, coming October 14th (or is it 24th?) on the Xbox 360 and PS3. In it he finds that not only was the game built from the start with online drop-in, drop-out co-op where each player can be on opposite sides of the city if they want, but it also led to some very satisfying emergent gameplay.

Back just after GTA4 launched my brother James would tell me he would run around the city with a friend of his in Free Play mode and blow away anyone who answered a cell phone on the street. Funny and cathartic, yes, but with no way to immediately segue into the missions like you’ll be able to in Saints Row 2 it was a bit clunky to do something productive when that got old.

Check it out at Co-Optimus.