I think the formation Barcelona started with (which looks like a diamond) makes them too dependent on Messi in the playmaker position. Sure he's a brilliant player but he wasn't at his best Wednesday. Fortunately their fullbacks provide width like nobody else, so it gives them an alternate attack in the formation. I think that with the rise and rise of Messi, the team is becoming more dependent on him.
Arsenal did a lot right this game, but their offside line, while the right idea, wasn't executed particularly well. They were lucky a few times. Like the 2 goals Ibra scored at the Emirates last year, they played the high line, but then gave the Barca midfielder with the ball too little pressure, allowing him to pick out the through ball.
Offensively Arsenal wasted too much time trying to short pass their way through midfield, which just invited pressure and kept costing them possession. When they played longer balls to the front lines. I think that's why Bendtner was put on. They bypassed the pressure and exposed Barca’s weak(ish) defence. The Arsenal Plan B highlighted in the recent Everton game paid dividends here, under slightly different circumstances. This was augmented by Wilshere’s runs through midfield. I don't know why I never realised how strong he is when running with the ball.
Finally I think Barca, as good as they are, are becoming a little too predictable for top level competitors. Pep will have to figure out a way to adjust his formation or tactics for Carnival Tuesday. Arsenal is still obviously a work in progress, but their progress is undeniable.
Barca's line up is confusing and I'm not sure it it's a traditional diamond, and some would argue that they often have no real out and out forward... Even D. Villa who is their most out and out forward takes up a wide withdrawn position. Messi, Iniesta and Xavi are the creative engines - Xavi the purest playmaker of them all, with Messi being the most advanced, and sometimes even as a pure striker... Along with the wingbacks, Pedro gives width to the midfield creative trio and is a more direct type of player...Busquets is the protector. If Puyol was fit, Abidal and Alves would be the wide threat...but instead it's Maxwell who to me is neither here nor there as an attacking wing back - I think Arsenal benefitted from that.
Barca might be predictable in what they do because they don't have the big man option and they don't stray from their core philosophy in building the play up...but they are certainly not predictable in how they do what they do...the angles at which they attack and the runs they make are pretty confusing....The big difference was that in the Arsenal game after they were one goal up they didn't go for the jugular and exploit the forward channels in a direct enough manner, and many times I think they let Arsenal off the hook after the play broke down by being a bit too casual, and not direct enough...I expect that will change in Camp Nou. Arsenal will have to play the same game they played at Emirates, disciplined at the back, and speedy in attack...just finish a bit better....Whether or not you get the lucky breaks is under no one's control...
No it’s not a traditional diamond. It just looks like one. They play a narrow 433, but when they play teams who have a high offside line, one forward (normally Messi) drops off a little to lure a center back higher up the pitch. This leaves a big gap in the defences offside line to get through balls for the other 2 to run on to. Barca destroyed Espanyol 5-1 earlier this year doing that. They also did it a few times in the Madrid game. So Messi isn’t a playmaker in that formation, like Seedorf on Tuesday. I guess it’s a type of 4312, which is broadly similar to a diamond. The difference is that in this, the -1- is not a playmaker, but a forward who drops deep to disrupt the offside line. The similarity to the diamond means that they depend on the wingbacks a lot, and yeah, Maxwell is no Abidal, but he did a decent job.
Any team that uses core beliefs or systems becomes predictable eventually. Guardiola has been brilliant at tweaking it to counter different responses to it. And they are technically superb, which means it still works against most opposition. Arsenal, as you said, has to stay disciplined at the back, but they need to put more pressure on the Barca midfielders instead of standing off. And yeah, van Persie needs to bring his finishing back up to it’s usual level. Walcott too. He’s regressing in that department.