For a defender, a nack of leaving things exposed at the back is quite a critical flaw, despite all the marauding he may bring to the team.
Vermaelen is a bit overrated IMO. Bit like the Eduardo situation really. The heart grows fonder in absence and all that.
I don't doubt Vermaelen is made of the right stuff but opinion of him is based on Autumn 2009 when he scored a freak amount of goals and had his honeymoon period. He's still got it all to prove.