Jeff Bagwell, who was never thought to become one of the greatest power hitters of all time, went on to do just that, putting up 79.5 WAR as a first baseman for the Astros in fifteen seasons. His rookie year was OK, and he won Rookie of the Year with a solid .824 OPS. His sophomore season wasn't as impressive, but he still put up a .812 OPS and played in all 162 games that year for the 'Stros. From 1993-2002, however, he put up an OPS of under .900 only once (.894 in 1995) and was the MVP in 1994 after putting up a 1.201 OPS, which is, obviously, ridiculous. His fantastic batting eye and hard-swinging approach did net him a lot of strikeouts, but nearly as many walks (1401 walks to 1558 strikeouts). There was even a time where he had decent speed on the base-paths, swiping over 200 bases in his career and even stealing 31 in 1997 and 30 in 1999.
Bagwell would have been a first-ballot Hall-of-Famer if not for all of the steroid controversy surrounding his era. To be fair, Bagwell was putting up his big numbers before the huge Sammy Sosa and Mark McGwire years. But steroids were already filtering through baseball clubhouses, as Jose Canseco later revealed in his famous book. But unlike many other players, Bagwell and Mike Piazza were only "suspected" to have used them. There was never any proof that Bagwell used performance enhancing substances. Unfortunately, the suspicion alone has kept both he and Piazza out of the Hall, and that's unfair. Bagwell is one of the best pure hitters of all-time with 449 HR and a career .948 OPS. He wasn't bad at all defensively at first base and he had more speed than a typical first baseman. He belongs in the Hall.
As for the Red Sox, they did enjoy eight years of Mo Vaughn, who compiled 24.8 WAR with the club. But Bagwell and Vaughn could have co-existed on the same team, and Bagwell was a better defensive first baseman. This would have meant that Vaughn could have played more Designated Hitter (DH) and actually been a bit more valuable overall. But the Astros got lucky and stole one of the best players the Red Sox ever drafted, and in the minds of many, should have been, and still could be one day, a Hall of Famer. Vaughn wasn't so lucky with his health after leaving the Red Sox, and the Red Sox have never had a first baseman of that caliber again. If the Sox had kept Bagwell, at least they would've had one of the best hitters of his generation and the Red Sox's destiny could have turned out quite a bit differently.
Photo credit: Wikimedia Commons user UCInternational