I love Brain Stew, it sounds so different to their other songs (and especially stands out on Insomniac where most of the songs sound very similar to each other) with the hint of metal, and just the slow structure of the verses with the "dun na, dun na, dun na" guitar gradually building up is really interesting. The lyrics are fantastic as well, I still remember seeing the first verse written on a school desk years before I got into Green Day and being impressed with the line "My eyes feel like they're gonna bleed". Also love it live, it's amusing how they've always poked fun at themselves for making a "metal" song by playing tongue in cheek metal covers to introduce it, the call and response with the guitar at the beginning is fun and the whole thing is a cool change of pace in the show. Never understood why it tends to be disliked so much, there's many more generic "typical Green Day" sounding songs that I'd call boring before a song that has so much more interesting stuff going on and sounds different to anything else they've done.