I'm having very similar issues lately..feeling good about my mixes... until i listen to Tool...then i assume my mixes are crap. I just spoke to someone at a well known mastering studio though, and the guy basically told me that as long as my frequencies are in the right places, they can handle the rest... I feel shitty about it because while i would love to send my album out there... its too damn expensive, and ultimately the way that I took it was... don't feel shitty if your mixes lack the shine... it can be polished in the mastering... (so now, i'm reading the mastering engineers handbook heh heh)