I said it before the game, you can't go to the Nou Camp and park the bus, with the team Barca have they will always score at least once. Despite the RvP sending off at most times you had ten or eleven players behind the ball, the only thing that happened was when RvP got sent off was you lost your only outlet, and it just led to the ball going straight towards your defence more often. Credit to Almunia and Djourou it could've been a lot worse without them, Djourou was on an absolute mission jumping in front of everything and Almunia needs no explanation.
Overall though you did get outplayed, badly. Arsene's choice to defend, defend and defend some more was silly in all fairness.
Said it after your cup defeat, you need to buy some new players, I said then you needed at least one better striker due to RvP's injury proneness and I also said you needed one or two top class defenders, and a GK. Although you can't fault them today, even if you had the best defence in the world I don't think you could've stopped the first and second goal and not conceded the penalty.