It's a slightly different way of playing normal PvP with a chance at purchasing some sweet looking gear. That's literally the most basic answer that should sum up Iron Banner. And for the people complaining about it, I see it as one of two ways. 1). The high leveled players are upset because they were expecting a face-roll stomp-fest in which they could dominate everyone lower than them. Especially non lvl 20's and low lvl 20's. Like this was supposed to be some kind of elitist cool-kids club or some crap. Granted it may function differently than what everyone expected, but it was never specifically described how it would function. Just that level and gear would be influential. Or 2). People saw this as new content and were mad because it's the same stuff but with a few different twists on it. I don't remember reading anywhere that this was new content. And how does this purposely restrict players to only playing one game mode? I'm not sure I fully understand that point. There's patrols, strikes, regular Crucible, VoG, daily heroic missions, and weekly nightfall missions.

Restrict them as in control is the only game mode for it