You didnt deserve anything from the game, as EVERY pundit has stated. It was a very close game, but for your superior possession you never looked like scoring. Yes we set our tactics out to beat you. We've done that every time we have played for about the last 4 years. Isnt it about time Wenger learnt to counter it. That would be a bigger worry for me if I was an Arsenal fan.
The penalty was a dodgy one, but it was missed so justice was done. It probably buoyed you more than anything so ended up working in your favour.
Bottom line, you didnt have a plan B when United didnt play the open game you require a team to play in order to compete. Unlucky but it decides nothing, dont worry about it too much!