Josh Beckett is, in my opinion, one of the best pitchers in the game because of his ability to not only dominate in the regular season, but in the post season as well.
Many players in the Major Leagues will be unanimous MVP or Cy Young choices, but when playoffs come, they're just bad. I'd like to use Alex Rodriguez as a poster boy here.
A-Rod had a great year in 2005, as he jacked 48 long balls, stole 21 bases, and ended the year with a great .321 batting average. The postseason was a different story for Rodriguez that year. He hit .133 in the ALDS, with no home runs.
Basically, Rodriguez had an amazing season, but threw it all away because of his inability to perform under pressure in the playoffs.
Josh Beckett, on the other hand, is the kind of player who can dominate the regular season, and then carry a pitching rotation throughout the playoffs. He did this with the Marlins when he won a WS with them. Beckett's career regular season ERA is a solid 3.80. It's not an amazing ERA, but given what Josh has been able to do when healthy, he will look to improve upon that number.
More impressive, however, are his postseason statistics. He has compiled a 7-2 record with a 2.90 ERA, while allowing only 3 home runs home runs over 87 total innings.
Beckett just has a killer instinct which allows him to control games under pressure, whereas guys like A-Rod thrive outside of the weight.
This ability separates the good from the great.