In response to the above things - we're hitting on some invaluable bits of information regarding mixing here.
Something I have found with a lot of people, both pro's and non-pro's. Also - in my opinion the cause for the often heard remark "the demo, or rough mix, sounded better". Over processing!!!
You start a mix - you add a bit of this, then because of this, you need to add a bit of that to the other - and so on. Before you know, you have introduced so many extra elements that you are really pushing it - and have to start cutting frequencies etc in order to avoid "mush".
Another resulting effect, your song starts, rolls and finishes, everything at one level, dynamics gone.
How do you solve that problem?
First of all, track a sound the way you'd want to hear it on a recording, and spend time doing it. If it is not exactly how you wish to hear it - there IS something wrong. The best recordings require NO processing, they are easy to mix and are transparent.
Its all about you input chain, microphone placement etc.
If you think about it in logical terms, all processing equipment is designed originally to either add stuff that should have been there in the first place (in an ideal world), or to correct / take out mistakes.
So, place a great deal of care. time and emphasis on tracking. The term "we'll fix it in the mix" is the most often heard piece of bullshit - it you have to fix something in the mix, that means you screwed up whilst tracking. It often better to re-do something like that the way it should have been done in the first place, than to try and fix it with extreme processing and / or EQ applications.
Secondly, take great care in applying processing. I have seen so many instances where processing is just fighting to be heard.
Example:
This is a nice reverb, I'll put a bit of it on this (so now you've added the sound of the reverb on your recording). This reverb is so cool, I'll add a bit of it on this and this as well (now you've got three same reverbs fighting for space). Hey! Now I can't hear the first verb all that well, I'll boost it a bit (cool, the fight continues). Ehhhh, 'coz I've boosted the first verb, all the things I've put the verb on sound like they are competing in the same frequency bands - I'll add some EQ.
See what I mean? I know 99.9% of you do this, realize it or not. If you had not been such an idle bastard and made sure your sounds each had their own space to start off with, or spend time designing a verb for each track individually, you would have required much less reverb, much less EQ
Just something to think about when you're mixing