I've done it before in active MMO's. I tend to find co-op more rewarding than competitive play at times. Even in more simple games; such as Farcry 3 (which by way was an AWESOME game). Bungie has a lonnggg history of implementing revolutionary multiplayer improvements. I remember being blown away by Myst way back in my PC days. Incredible advances for it's time. They've already stated that a major portion of this game will entail 'seamless' co-op with friends n' strangers alike. I'm VERY sure Bungie will deliver an environment that motivates the most lone wolf of players. This will likely be achieved by speed (quick, effortless matchmaking) & reward (for example: A unique token that may be traded for rare items even if no mission loot is desired/needed).