mellow in places, rocks out in places.  BUt what this cd is is always strange and unpredictable.  It is quite likely that you will never hear a weirder or more truly disturbing cd than Tool's Aenima.  This is the least straightforward cd ever made in the popular music scene (I can't speak for college radio or underground) and it is incomprehensible at times, boring at times, and thrilling at times.  There are a good number of tracks that have a strange sound that really hurts your ears as it builds, then it goes into a normal song.  Many songs are haunting and depressing.  However, if you expect something like the Cure's Disintigration or something, you are in for a major surprise.  I would suggest you get Undertow before this cd, its much more accessible.  but do check this music out; it is quite disturbing and frankly, too stale in bits for most people.