Most underrated players in baseball?

The big problem with all this is that, like you said, it doesn't apply cross-era because that wouldn't make sense. It's simply impossible to compare eras without engaging in unverifiable speculation. I like OPS+ because a players greatness should be viewed in context; Carl Yastrzemski's line of .301 average, 23 HRs, and .921 OPS would make him a decent power hitter today, but in 1968 he was the league's dominant hitter with those numbers. You can make a few arguments to make Babe Ruth seem less impressive (end of the Dead Ball Era, no non-white competition, etc.), but Ted Williams put up pretty much the same OPS numbers as Bonds while playing in an era in which the rest of the league didn't hit as well as they do today. Unless you subscribe to the notion that hitting a baseball is harder today than it was back then, which I don't, this tells us that Williams was a better hitter. Throw in the steroid issue and the fact that Williams lost some of his peak years to World War 2 and Korea, and I think the case for Williams being the greatest hitter ever is pretty solid.

This post got way too long. Good night.