Both of these bands received Album of the Year "honours" from me (Mogwai '99, Xiu Xiu '04), stayed on a hot streak for a few years (according to me, and the judging by the praise and attention they received in the music press) and eventually sunk into a rut of relative indifference. Only their fans take notice when they release an album these days, and although that's not so unusual when you've reached your eighth (Mogwai) or ninth (Xiu Xiu) album, they've also brought it on themselves by happily confining themselves to their own little microgenres and releasing essentially the same album several times over.
The problem with Mogwai post-2003 is one of diminishing returns. They can write these keyboard lullaby tracks like "Heard About You Last Night" in their sleep these days, and the results were a lot better the first few times they recorded them ("Take Me Somewhere Nice", "Hunted By a Freak", most of "The Hawk Is Howling"). After a few false starts (e.g. "My Father My King") they threatened to become a full time metal band around the time of "Mr Beast", but outside of a few killer tracks where they got it exactly right, they proved to be average at best at doing metal, and at this point the novelty of hearing them aim in that direction is long gone.
There's a noticeable lack of loud guitars on this album. "Come On Die Young" is still their quietest album, but it was packed with tension and built toward thundering climaxes that paid off the patience of the listener. There's no payoff, no final destination to "Rave Tapes". You can be quiet and still be intense, which "Come On Die Young" pulled off beautifully, but "Rave Tapes" is mostly no-frills easy listening -- I keep putting it on and 90% of it simply fades into the background as I go about whatever else I'm doing.
The best thing about "Rave Tapes" might be the album cover, and it's too bad the music didn't take its cues from 70's prog too ("Remurdered"'s not to Krautrock aside). The experiment might not have worked, but it would have been an interesting risk worth taking.
I'm not sure why it took so long for Xiu Xiu to morph into Suicide. The elements were always there -- robotic, jackhammer beats; lo-fi electronics and blistering, often uncomfortable noises, and a charismatic frontman with a half speaking/half singing delivery that becomes an acquired taste. All that was needed was to take the extra step, go full on "Rocket USA", and churn out songs like "Stupid In the Dark" and "The Silver Platter". And from there it's a quick left turn into 90's Skinny Puppy on the industrial squelch of "Lawrence Liquors". Elsewhere, "EL Naco" is like Speak And Spell-era Depeche Mode after it's been left out in the arid desert to rot, its once sunny synth pop tones having long since been taken over by madness.
Jamie Stewart's vocal and lyrical styles remain as twisted and unconventional as ever. "Black Dick" has a chorus that consists of just those two words repeated (or rather, stuttered and spat out) over and over. "Cinthya's Unisex" finds him huffing mind bending lines like "Oh God, you're so confused when you're ... cute", and losing his mind with screams of "nononononono" and seconds later "yesyesyesyesyes". Then he throws a tantrum over hickeys, as if he's poisoned by the memories of them, and finally ends up whimpering "I hate everyone but you" helplessly a few times as the machine drum beats pile on relentlessly. And "Botanica de Los Angeles" might be Xiu Xiu's best "pop" song since "I Luv the Valley OH!".
Xiu Xiu are can still be frustrating, because their tendencies to shock and be abrasive can overwhelm their songs. But they're challenging even their most devoted fans to buy into what they're doing, that's for sure. They're trying, which is more than you can say for Mogwai.