Two things need to be sorted out:
we tend to lose control after opposition goal, it happened many time now. We are champions team that won everything, shouldn't lose our heads this easy. We played a good first half, we looked better than them, like we'll score againg and then falling appart.
Second, and most important, thing is defence. But like some here I don't believe our problem is last 4, even though we of course suffer with injuries. But our defending as a team is bad. I thought Lucho had a plan in first season. In my opinion he wanted us to defend slightly deeper than with Pep and press on our half. Not a bad idea, we are compact, not so tiring and also leaves room for counter. But now we neither high press neither defend deeper. We have a high defensive line, our front 3 stands up high with Suarez trying some "suicide" pressing against 3 players, Ney and Messi standing, then our mid of course gets bypassed easily as we go 4+2 full backs against our 3 mids and then our last 4 needs to save the day. Every attack for them is a counter with players runnig in speed towards them, even if it wasn't counter but positional attack. It's impossible not to concede that way...and I'm affraid what teams that pack a punch can do.
No need for Messi to run much more, neither Ney or Suarez but we are either going back to high TEAM pressing or drop back. In that case Suarez and Ney must come to midfield line and form a line with 3 mids with Messi floating and lurking for a ball withoout too much commitment, then we can form 2 walls with defense that will be much harder to pass.