I’m just listening to my favorite Led Zeppelin album, III. Both sides are clearly different, the first side electric hard rock and blues, while the B side is acoustic folk, and both sides are great. The first example I can think of is Bob Dylan’s first electric album “Bringing It All Back Home”, with the same split on A and B side. Another great one is Neil Young’s “Rust Never Sleeps”, this time the A side is the acoustic one while the hard rocking songs come on the B side. All these three albums happen to be masterpieces IMHO, so what have you?
Would Dog and Butterfly by Heart be along the same lines?
One side is the Dog (rock songs) and the other is the Butterfly (ballads)