Just love the way he cushions the ball. Every pass he receives stops dead- on Barça, only Messi, Busi and Xavi have that degree of killer touch.
As far as contribution, it's not all about flash bang whiz dribble assist score. Watching today, I think people are under the mistaken impression that it's Barça's offense that make it superior to City (and other teams). While (Messi) the offense (Messi) is (Messi) scary good (Messi), Barça's defense is what makes the team so formidable. By defense, I'm not talking about the back line, but the pressing/positioning/possession that grants the opponent only occasional (and usually impotent) whiffs of the ball. Let Man City have as much of the ball as Barça, and their attackers have more than enough quality to score. But Barcelona just won't give them space to construct anything. Boot and chase is actually a valid tactic against Barça, since it has a better chance of getting the ball in Barça's half than trying to pass it out. For an attacking team like Manchester City to be so overwhelmingly controlled by an opponent has to be doubly frustrating.
Which all goes to say Iniesta is still a perfect cog in that Barça spider web of expert technique than enmeshes the opponent. Whether or not he has a statistically flashy game is irrelevant, as long as the team is creating scoring opportunities and denying them to the opposition. Unlike other teams, Barça rarely makes costly mistakes from poor technique; more often, a Barca player has a moment of arrogance that an opponent takes advantage of (like Messi's casual reception of the pass today, which lead to the City goal), or Busi's cute moves, etc. One might say Iniesta is generally more cautious (perhaps slightly less than Xavi, a desire to protect the ball at all costs), but his judgement is usually excellent about when to take risks and when to control the game. His lack of arrogance might be at the root of why he's not more aggressive and in the limelight, but then you need some balance on the team.
Lovely performance, including some tiki-taka with Neymar on the left which we haven't seen much of to date (always ended too soon).