There are a few that comes to mind.
Pouliot always looked like the real deal with some moves he did
... but in the end, he was very inconsistent and taking bad "revenge/retribution" penalties.
Bonk had lost a step maybe, after the 05-06 lockout, speed was the name of the game.
Yeah, Samsonov, had broken his wrist real bad in Boston (while playing for them)... never got as good as he once was...
Current : If Lekhonen can start producing early, it'll be nice. Still, if he is to be a slow starter who produces late in the season (as the 2 last years) + playoffs (a few goals against the Rangers in '16), I'll take it. But early during the his first 2 seasons ... disappointing. Volume shooter though. I could see him score more if Pacioretty was gone, would replace him with the lots of shooting at the net.
Drouin... I have seen often guys with LOTS of talent but over average production only. I think Galchenyuk was about a similar mold, except less skating and better shooting.
About PK... I changed my mind about a thing. When he got injured, I thought he should have already been taking out of the lineup with all the mistakes he did, trying to do too much. Now, if I put myself in his "skates".. I think like "I got to do something otherwise we'l lose again"... so doing too much he tried.