Not sure how people can mention late rounders as prospects who fell through before they even played in the NHL.
to me it would be Kulemin and Frattin. Kulemin had an amazing season, driving the net for goals and looked to be the perfect 2nd line winger two-way player type got 31 and then 36 points in his first 2 seasons, then 57 in his third, really thought he was progressing. His offence has regressed considerably since then and he's more of a 30 point player at best now. Not worth anywhere near his contract as hes a 3rd line player.
Frattin had an awesome start to his NHL career and looked great in the shortened season, he always had the speed, always seemed to get breakaways and had good chemistry with Kadri. He never progressed and his offence completely dissappeared, went from looking like a 2nd/3rd liner to a borderline NHLer.
Overall, we havent had a major bust though, more like late rounders that played decently but never exploded, which kinda shows how poor our drafting is, we rarely draft a star.