Very difficult question. His early career was so amazing, with wins at the BCA Open, the All-Japan Championships, the Sands Reno and the US Open by the age of 24. He'd also been a Mosconi Cup MVP by then. For this reason, the expectations were high, perhaps unfairly high.
When the soft break was allowed, Corey probably was the world's most effective breaker at nine ball, but the soft break was banned by about 2003 and, once deprived of it, his fortunes changed a bit for the worse. It must be further noted that this was about when the level of international pool skyrocketed, with the talent pools in both Europe and Asia growing dramatically. The major titles weren't very numerous for Corey after all this, though he still had occasional moments of incomparable mastery. Major titles have largely eluded him over the past decade, in particular.
All of that said, though, Corey won both the One Pocket and Bank Pool titles at Derby City, two supertough events to win, so his credentials as an all around talent are beyond doubt.
Did Deuel live up to the expectations or potential that we all saw from 2000-05? I'd say no, but he's had a great career, and a Hall of Fame career at that. He'll, quite sensibly, be remembered as one of the greats.