In my view, the most important factor was Bayern's ease at keeping possession - and also how they cancelled out Rooney (apart from the opening goal). Neville's age/lack of speed showed and it doesn't look good for the second leg.
Barcelona also hold on to possession - even more so - and, tonight, Arsenal will have an up hill struggle against the Champions (World and European), even at the Emirates.
Mainland teams in Europe have caught up with those in the Premiership and their national teams will do well in the World Cup - with the help and experience that many of their players have gained in said Premiership.