Drouin had a pretty good season at first, then stopped producing and came up way short of the expectations when the going got rough and defenses started paying extra attention to him. This lack of production made one thing clear to me and that is that his position as an NHLer is that of a passenger, ala Pacioretty. He is simply just not one to drive a team into the playoffs, but someone who can be a pretty good secondary offensive option on a great team.
Now, if you want to call Drouin a bust because of his past draft status, despite him managing to score 50 points, be my guest and do it but I wouldn't though. He is a pretty flawed player, one that isn't consistent at all, but he still has offensive talent and tools that could see him post pretty strong numbers if he ever figures it all out (though I'm not holding my breath for it at this point).
In the end, he is a 50+points a year guy, with the potential to hit 60+ with a better powerplay, not one that you can build a team around, but still a pretty good player despite his warts and lack of consistency. The hate people have on him is partly justified by his soft play, but also quite overblown.