The problem with most (90% of "remasters" of old material and 90% of new releases) is something called the "Loudness War". You can watch this short video to understand this and why it's bad for music:
http://www.youtube.com/watch?v=3Gmex_4hreQ
There are many reasons that are "forcing" mastering engineers to make extremely LOUD masters with zero dynamic range, too many to go into. Artists want it LOUD to be "competitive" with the latest release from a competing band, record companies want it LOUDER to jump out of the radio, or to be the loudest thing on your iPod to make you stop and listen.
The problem is that to the average guy on the street, LOUDER is "better" (shown time and again in blind studies). So, to the average guy, remasters are better precisely for the reason many audiophiles hate them.
For us audiophiles, many of us are re-discovering and re-evaluating the ancient mid-80s early first CD pressings of music titles. In many cases, they are honest flat transfers of master tape. There was no way to compress the music back then, and engineers applied very little EQ so you get to hear the master tape warts and all.
There are newer technologies ("No-Noise") which strip out the tape hiss on analog recordings. Average guy on the street complains-- "hey this old Miles Davis recording has tape hiss- YUCK".
Well, what did you expect dumb-ass? So No-Noise gets applied which KILLS MUSIC. You can't just strip out tape hiss, you also remove elements of the music. The result is a canned, phony "digital" processed sound. But hey-- no more tape hiss...
So, here we have modern digital equipment that in the right hands could be producing legitimate remasters of older recordings and making them sound MUCH better than the original CD versions from the mid-80s and the Dark Ages of digital.
But wrecking this potential is the current need for mastering engineers to use hyped smiley faced EQ and worst of all, COMPRESSION to maximixe the LOUDNESS allowed by 16-bit CDs and then stripping out tape hiss with No-Noise.
It's been argued that most modern CDs are "defective" because they contain no dynamic range at all.
The other problem is that the current generation who have only been listening to music since the mid-90s knows of no other world except that of MAXIMIXED, LOUD CDs. That sounds "normal" to them, and older CDs will sound too quiet and distant and muffled.
To them I say-- it's called a VOLUME KNOB. It is your friend.
P.S. This is why labels like Mobile Fidelity and Audio Fidelity (Steve Hoffman) exist. When you buy one of their expertly-mastered discs, you are getting the most honest presentation of the music, prepared by the best people in the business.