Returning from a 16-year absence, Celtic Frost begins Monotheist with an invigorating two-song punch that hearkens back to the band's classic thrash and simultaneously updates it. Initially, this sounds like the wiser, more powerful unit you'd expect, considering that leader Tom Warrior never stopped exploring his creativity or contemplating approaches to his band's sound. But, as fans are well aware, Warrior and returning foil Eric Ain simply can't sit still. Practically worshipped in thrash and black-metal circles, Celtic Frost has also confounded expectations before. Monotheist presents many shades, mostly between doomy riffs and thick keyboard gloom. However much this recipe entices you on paper, bet on feeling uncertain in many spots which, it seems, is exactly what Ain and Warrior want.