Since I have been a fan, there have been several players with huge expectations in the Red Sox minor league system. Some of these players, such as Mo Vaughn, Nomar Garciaparra, Trot Nixon, Jon Lester, and others meet those expectations. Others are not as fortunate.
Michael Coleman was expected to be an all-around talent. He could do anything on the baseball field, run, hit for power, play defense, etc. He even had the nickname "Prime Time", which was also Deion Sanders's nickname. He was expected to be a great player. It just did not work out that way.
Coleman was selected in the 18th round out of high school. He cracked the Top 100 prospects list in 1996 and made it to #51 in 1998. He had a 20/20 season for two minor league levels in 1997 and hit 30 home runs in 1999 for Pawtucket.
Coleman made his ML debut for the Red Sox in 1997, but only played in eight games. He played two more in 1999. He spent several seasons in AAA and the Red Sox eventually tired of him not being able to take the next step forward. Coleman was traded to the Reds along with fellow failed prospect Donnie Sadler before the 2001 season for Chris Stynes. He was traded again during Spring Training along with the whining Drew Henson to the Yankees for Wily Mo Pena, which turned into a hell of a trade for the Reds.
Coleman played 12 games for the Yankees that year and was released. He went back to the Red Sox where he again failed to make the Majors and bounced around the minors for a few seasons after that.