The one hundred twenty-third album: #123 Iron Butterfly - In-A-Gadda-Da-Vida
Iron Butterfly was a clear example of the rock bands as they were in the late 60s, incorporating an organ for that psychedelic feel with the heavier guitars that lean towards what became hard rock and metal. The vocals are appropriately gruff, the guitar riffs often fairly simple, with the organ adding the flourishes. The lyrics mostly feel fairly tame - still love songs and normal life songs, nothing rebelious or out there, which feels simple. The first half isn't overproduced either - these feel like songs that can be played easily at a concert, something not all rock of the time can claim.
The second half is a single seventeen minute song - or jam, really - with some lyrics but mostly showing off the instruments and creating a whole song. It feels like an early anthem, an ongoing hard rock sound that keeps going while still staying interesting. It's a sign of hard rock and metal, something this may have influenced, but certainly where rock is going towards.