I haven't heard 'OPIUM' so I can't compare it but I feel this album is a real step up from 'WITCHAZEL'. Don't get me wrong, I love and cherish 'WITCHAZEL' but 'KILL THE WOLF' is a much more focussed and dare I say, mature album. There's still the whimsical humour and nods to Prog and Psychedelia, just not as much, making it sound more serious as a whole and flowing in a more structured way. Whereas 'WITCHAZEL' made me grin on first listen, 'KILL THE WOLF' made me think...and then grin...a lot! Anyway, buy it because you won'y be disappointed, promise.