He is having a career year in points, rebounds, steals, shooting percentages, etc. We don't even know if it is sustainable yet, for all we know he will regress for the rest of the season. But still, we are talking about a complete out-of-nowhere renovation of his game. So it's disingenuous to say that it was a "big miss," because based on the way Blatche had played the last 7 seasons there was no reason to want him besides size.
Aside from the FG%, he isn't having a career year. Per minute? Possibly. But per game, he isn't having a career year.
And his game didn't go under a complete renovation. This is the same Blatche that was playing a versatile role in the Wizards before he decided to give zero attention to his on-court performance.
That's the whole point of a surprise draft pick or a surprise MIP-candidate, it's a SURPRISE. Every team passed on Blatche, reasonably considering his career up to that point. The Nets took a gamble, and it ended up working out because he had an amazing turnaround in his level of play. They got lucky. It happens sometimes. But then using it as a flimsy excuse to attack Danny Ainge for somehow not being able to see the future is pointless.
It was a gamble, but not in the sense of expecting him to play good basketball. Before the last season's turmoil, he averaged 16.8 ppg, 8.2 rpg, 2.3 apg and 1.5 spg for the Wizards. Granted, the Wizards were still terrible back then, and Blatche's field goal percentages weren't decent enough to call him great (44% FG isn't desirable for a C, even he is taking outside jumpshots).
Nevertheless, it's not like his performance this season came out of nowhere. He was already capable of it, that's why the Nets took the gamble.