One of my earliest loves. Not sure which of the iconic parts, vocals, bass or guitar, really sells it, although of course the guitar fill (bleep bleep bleep bleep bleep bleep) has to be the signature motif.
"I've been asked a lot over the years how I did the 'beep beep' guitar parts on Spirit, so for any guitar players out there who would like to learn how, try the following: Using a 2-pickup Gibson, set the neck pickup volume to zero, bridge pickup volume to max, with the pickup switch in the middle position (with Gibson wiring this gives you silence in the middle position). Do a string bend, picking the B & E strings together with one hit, just ahead of the beat, then use the pickup switch to kick in the bridge pickup in triplets (6 per bar) as you let the B string bend down two frets."
That track is aural crack. I'd discuss other tracks that have transfixed me as much, but apparently the world is ending so I have run out of time.