Loudness

In August of 2006, music legend Bob Dylan made some controversial statements decrying the state of modern recorded music, particularly as relates to the overcompression frequently used by studios to make records sound louder on the radio.

A number of music producers have begun rallying to the same cause, noting that:
Record companies are competing in an arms race to make their album the loudest. The quieter parts are becoming louder and the loudest parts are just becoming a buzz. This could be the reason CD sales are in a slump.

Whole layers of sound are missing. It’s because record companies don’t trust listeners to decide themselves if they want to turn the volume up.
Britain’s leading studio engineers have launched the campaign to make records range in levels. To explain, dynamic range is the difference between the softest and loudest sounds on a CD. Using compression, producers can minimize this difference and the result is that albums sound louder, even at lower volumes.

Interestingly, due to technical limitations of vinyl, this kind of "loudness-based" mastering is not possible, and the records tend to sound better than their CD counterparts.

For more information on this, you can check out this article.