David West was the can't miss prospect in the mid to late '80s for the New York Mets. He started the International League all-star game for two straight years before the Mets traded him to the Twins in 1989.
In return for David West, Rick Aguilera, Tim Drummond and Kevin Tapani, the Mets received Frank Viola. Viola was supposed to be the missing piece for the NY Mets. He had a 2 1/2 good seasons with the Mets before moving on, but couldn't bring the Mets to the playoffs.
In three full seasons with the Twins, West went 12-16 with a 5.16 ERA. He never became the ace of a staff as projected.
Ironically, West did win a World Series ring with the Twins in 1991. He was also part of the 1993 Phillies who lost to the Blue Jays. Frank Viola never made it back to the post-season after he left Minnesota