Just remember, the only reason Benfica (and Di Maria) had it so easy is because the Portuguese FA cheated and helped them to the title - Benfica won something like 15 red cards or something INSANE like that, also Hulk, who was Porto's best player during the start of the season, was suspended for hitting an official, but instead of being properly tried the court waited 3 months during which he was suspended and nothing was happening, and really, Benfica had an easy season. In Europe they were good at times, but Di Maria didn't play well against the big teams.
I believe in Di Maria, if you see my comments from pages before, i think he's good.
BUT.
I also think that some people get carried away, and forget to factor in that he had a horrible 1st season at Benfica, he had a good season this year but he wasn't the most consistent (Falcao and Cardozo were much more consistent, for e.g.) and also that there were external circumstances that helped Di Maria and Benfica.
And finally, just cause he's good in Portugal doesn't necessarily mean he'll be world class outside of the Portuguese League