In the early years of gaming, playing was all about getting that high score on the arcade machine that everyone else would see and revere. Making it through 574 identical levels of Pac Man meant that your score would hang out in infamy for quite some time, giving you bragging rights and a sense of superiority over other gamers.
These days, games rarely keep score. The content and format of most games are not conducive to such a tally, and as such, they have been replaced by other rewards. On Xbox360, the Gamerscore is the amalgam of all individual reward points earned in all games attached to a single Gamertag. This score carries with your avatar anywhere you go – online play, websites, or other friends' consoles. It is the ultimate "nerd cred."