Indeed, the Real Madrid match in Spain was a big turnaround. It shouldn't have been, really, because funnily enough he hasn't shown that day anything new - great shot stopping and being a bit dodgy on crosses. But for whatever reason it seemed that performance in a big game started changing a lot of minds.
Perception is a bit silly sometimes. People form and opinion and stick with it, even when the reality changes (Rafael also needed time in order to get recognition). But then something happens and it all changes.
Anyhow, De Gea deserves all the plaudits. In the last couple of months he has really shown impressive improvement in dealing with crosses. Overall, despite all the chopping and changing in the first halves of both his seasons here, he really took over for the closing months of 2011/12 and 2012/13. Could have been two championships for him and the fact it's not, is not really down to him.