So, to answer the OP exactly: no, there isn't too much criticism.
The criticism from Scotland fans is far greater than that of United fans - even his love for the GERS still gets criticism because they think he is a poor football who plays up top for Scotland. The WiKi stats say no goals in 14 games. For me they see what some of us see - just an awkward looking/playing footballer.
For me, i'll echo what some others have said/written - he isn't Premier league quality and grossly over rated at £18m. We had to buy someone at the time and Swansea held out for what they got - fair dinkum to them - it isn't a crime for some of us to not think he is nothing more than average.
Swansea played with wide players - we don't play the same way, so I certainly have sympathy with him for the lack of service.
He wouldn't get any where near a starting place for me.
UTB