I think everyone will say Darko, but I still beleive he was in a tough situation and could (not will) become a pretty good player. Still a dissapointment though.
To me dissapointments were Reece Gaines, Collison (injury), and Pavlovic (Utah) a little, and Banks a little also (Boston never had a real PG). Carlos Delfino, can't say yet, but he could become like a Ginobili when he comes (thats a good thing).
Mispercieved dissapointments
Some might see Sweetney as one, but if you watch him play and see how he's been doing when getting minutes then you know he's not. Troy Bell also, but he was behind White Chocolate, and Watson.
Pietrus might also have been seen as one, but that was just injuries, and look whats he's been doing since he can back. I really like Pietrus, so much upside, he can shoot, is atheletic, a get down and dirty defender, and he can also pass and handle the ball pretty well.
His stats as a starter this year: 9.1 points, 3.7 rebounds, 0.7 assists, 0.93 steals, 0.57 blocks. 45.7% FG, 27.9% 3PT (he's better than that), 72.7% FT, 25.3 minutes
The thing is that Dunleavy will have to move to the 3 later, and J-Rich is the 2. Pietrus can't play the point, and Speedy is there anyways. I really think he can be a starter in the league, but in GS, not likely, at best he'll be the sixth man with hidden talent.