Of course and without a doubt, one of their absolute best songs. To me easily one of their top three songs. I get the criticism that I've read sometimes that it's too long (a comment that I've read also for Kashmir, which is also one of their absolute best songs) but still it's a great song.
And I suspect, one of their most influential on metal with that galloping rhythm . Or at least I can't think of songs before Achilles with that kind of rhythm (there are a couple of tunes of Michael Schenker like Lights out but I guess those were made a year later, so I would not be surprised if Ufo and Scorpions were influenced themselves by Achilles)