A new album from Massive Attack is an event, even if only one-third of the original group is present for the festivities. Just the group's fourth album in more than a dozen years, 100th Window marked the departure of Mushroom (permanently, after artistic differences) and Daddy G (temporarily, to raise a family), leaving only one founding member, 3D (Robert del Naja), to muddle along with arranger/producer Neil Davidge (who made his Massive Attack debut on 1998's Mezzanine). Though Del Naja is mostly successful giving the people what they want -- a follow-up to Mezzanine, one of the most compulsive listens of '90s electronica -- it unfortunately comes as a sacrifice to the very thing that made Massive Attack so crucial to dance music: their never-ending progression to a radically different sound with each release. For better or worse, 100th Window has the same crushingly oppressive productions, dark, spiralling basslines, and pile-driving beats instantly familiar to fans of Mezzanine. Fortunately, it also has the same depth and point-perfect attention to detail, making for fascinating listening no matter whether the focus is the songs, the effects, or even the percussion lines. Jamaican crooner Horace Andy is back for a pair of tracks ("Everywhen," "Name Taken") that nearly equal his features on the last record, while Sinéad O'Connor makes her debut with three vocal features. Unlike Liz Fraser or Tracey Thorn (two Massive Attack muses from the past), O'Connor's voice lacks resonance and doesn't reward the close inspection that a Massive Attack production demands. Still, her songwriting is far superior and the slight quaver in her voice adds a much-needed personality to these songs. "A Prayer for England" is a political protest that aligns itself perfectly with the group that coined its name as a satirical nod to military aggression. Another feature for O'Connor, "What Your Soul Sings," is the only song here that compares to the best Massive Attack has to offer, beginning with a harsh, claustrophobic atmosphere, but soon blossoming like a flower into a beautiful song led by her tremulous voice. In comparison, the four songs for 3D are average at best, mere recyclings of the same ideas heard years earlier. That's satisfaction enough for those who kept Mezzanine near their stereo for years on end, but a disappointment to those expecting another masterpiece.