Of course he is. Look at how many goals he's scored against the likes of United and Liverpool. The season we reached the CL final, look at his perforances against teams like Real Madrid and against a Juve team that squad wise was the best in Europe and had the best defense without a doubt. I remember him making a mockery of Cannavaro and Zambrotta.
How is Del Piero more of a big game player than Henry is?