Source: ESPN: SportsCentury Evander Holyfield
I don't believe Evander Holyfield is an underrated boxer or an overrated boxer but he gets the respect that he deserves from the fans and media people who've covered his career and are familiar with it. I've seen most of his fights as a heavyweight because he became a heavyweight when I was in junior high and high school in the late 1980s and early 90s. He gets the respect that he deserves as a four-time World Heavyweight Champion and a warrior whom you literally had to beat the hell out of to stop because he didn't know how to quit.
Evander Holyfield was a beefed-up heavyweight unlike a Muhammad Ali, George Forman, or Larry Holmes, who were simply born to be heavyweight boxers as well as champions. Evander wasn't born with that type of body even though he was 6'2", which is a good height for heavyweight boxers, but was still fighting at 185-190 pounds in his mid- and late twenties and bulked up and got to 205-210 by the time he started fighting as a heavyweight because he was dominating the cruiserweight division as the world champion and needed bigger stronger competition, which is what he got.
Evander, not being the natural heavyweight that he was, had to go through a vigorous training program to put on the legitimate muscle so he could not only fight as a legitimate heavyweight but also as a strong, successful heavyweight. By 1989 he was not a knockout artist who could take you out in a couple of punches but someone who could avoid getting hit and take huge punishment, as he did against George Forman and Riddick Bowe, but also beat the hell out of you with a variety of different punches from a variety of different angles with great hand-speed and solid punching power.
One good thing about Evander's career was that he was in the prime of his career as a heavyweight in the last good decade of the heavyweight boxing division in the 1990s, which meant he was in a lot of great fights, and it's the warrior in him taking on these bigger stronger fighters like George Forman, Larry Holmes, Buster Douglas, Riddick Bowe, Michael Moorer, and Ray Mercer and later in his career, Lennox Lewis, that empowered him not to take on a lot of these fighters, but to beat most of them simply by always going at them and refusing to be beaten.