Overall, I thought the song, performances and mix were pretty good.
The drums seem to be a little buried in the mix, which might be okay for the style of the song. The drum sounds and performance seem to be very good, but the bass is "in yer face" for pretty much the whole song, while the kick seems to disappear in the busy spots. It still kind of works though. It seems that the vocal is well aspected as the "main feature", so more drums might screw that up - I don't know. If it were my mix, I might be trying to get a hair more out of the drums, probably at the expense of the bass and guitars.
I'm not sure that it was too bright, but I agree with the sibilance issues on the vocals. I'm not sure what the cause is - could be a mic or positioning issue with the tracking. She's a good singer, for sure and the vocals stand out very well in the mix but also seem to have the worst fidelity. Grainy. It's hard to tell at the RMS level the track was mixed to. Which leads to:
Dynamics!
The song still has good dynamic content to it. I get the impression that it wasn't crushed to death with a limiter, and indeed the valleys are there in certain passages which leads to good punch and impact. Thing is, when I listened to it in Cool Edit and looked at the meter, the over indicators were on constantly. This might actually be the source of the vocal problems. If the mix could be rendered again at 1 or 2 dB lower without actually changing any balances, or until most of those overs go away, that could help to clean things up for you there. I'd probably try that first, and then see if the vocals are still sibilant and look at some de-essing options. I've heard worse sounds coming off of CDs that were hard limited to the rails without actually having any overs, fwiw.
If you absolutely have to jack the RMS up that high, try using a limiter.
But it still sounds pretty good overall.
my two cents...
sl