By 1972's Houses of the Holy, they started becoming much more original, stripping away their blues for a more straight rock with progressive influences. A lot of people dislike their 1976's album Presence and while it's definitely not their best outing, the opener Achilles' Last Stand stands out as their crowning achievement for me. 10+ minutes of every single thing amazing about Led Zeppelin in their peak: Plant's mesmerizing vocals, Page's groundbreaking guitar playing which is made to sound like an orchestra, a crazy complex bass line from Jones and of course, one of the greatest drum performances by the one and only John Bonham.
The lyrics are also fantastic, evoking a huge mythological scene, going along with the title. Of course, Robert Plant improved as a lyricist over the years even though he could still nick blues songs for his own but by this time, when he felt inspired, he could write some amazing lyrics and this is an example. The feeling this song gives is one of the most epic feelings I can describe. I can never listen to this song and not feel amazing.