I know not everyone who reads this is a statophile like myselfa and is familiar with the statistics on Baseball-Reference.com. As I introduce more profiles, here´s a (estimated) reference list for OPS+ and ERA+. Notice the different scales for each of the statistics. This is important to consider because a 120 OPS+ is not the same in relative performance as a 120 ERA+.
200: Babe Ruth
190: Ted Williams
180: Barry Bonds
170: Albert Pujols
160: Stan Musial
155: Hank Aaron, Joe Dimaggio, Manny Ramirez
150: Honus Wagner, Jeff Bagwell
145: Jim Thome, Vlad Guerrero
140: Miguel Cabrera, Gary Sheffield, Duke Snider
135: George Brett, David Wright, Al Kaline
130: Wade Boggs, Roberto Clemente, Jason Bay, Chase Utley
125: Yogi Berra, Bernie Williams, Derrek Lee
120: Harold Baines, Joe Gordon, Shawn Green
115: Gary Carter, Raul Ibanez, Robin Yount
110: Andruw Jones, Alan Trammell, Frankie Frisch
For OPS+, there are 650 players that have reached a mark of 110 or higher (100 is league average for a given time). Notice even in each value tier how the skills of each player vary even though they have the same career OPS+ value.
ERA+ (career for starters)
154: Pedro Martinez
145-150: Lefty Grove, Walter Johnson, Ed Walsh
140-144: Roger Clemens, Johan Santana, Brandon Webb
135-139: Cy Young, Randy Johnson, Christy Mathewson
130-134: Roy Halladay, Carl Hubbell, Greg Maddux, Sandy Koufax, Dizzy Dean
125: Lefty Gomez, John Smoltz, Dazzy Vance
120: Jake Peavy, David Cone, Don Drysdale
115: Steve Carlton, Chuck Finley, Ben Sheets
110: AJ Burnett, Tommy John, Jerry Koosman
105: Jamie Moyer
For ERA+, there are 504 pitchers that have reached a mark of 105 or higher (100 is league average for a given time).
Another thing to keep in mind is that both these stats are adjusted for ballpark and era. Great pitchers from the modern era have very high ERA+ because this is one of the highest scoring eras in baseball history.
Again, these are just examples of tools to evaluate players. I use it more as a first impression for a player. You have to look deeper at individual seasons, circumstance (ballpark and era), splits, and other aspects to get a better sense of how good a player was....statistically. Not all measures are perfect, but if you find enough that say the same thing, then what you think is probably true.
What do you primarily use to evaluate a player´s career?