I think Barca not having their coach (he's getting treatment abroad atm) has hurt them to an extent, but as with last season, if you're totally reliant on Messi for goals and he can't get into the game then you're in trouble.
Teams that win the CL are by and large stingy with goals conceded and Barca haven't kept a lot of clean sheets lately, which is why I think Bayern are a great shout this time round. Madrid will be loving this too, if they can remember how to play against United in the 2nd leg.