The intro is one of a kind. Great drumming from Nicko. Amazing pre-chorus which is just a little bit better than the actual chorus. Good lyrics. The bass line is insanely good! Both solos are fantastic, especially Dave's one (that tapping is majestic, like in SOTC) - the little bass solo under that solo resembles the one in OTGDY and it is brutally good, of course. The screams (especially at the end of the song) are pure evil... Bruce, you're magician. One of the best openers in Maiden history.
This song's energy feels like a train - it starts off slow, gradually ratchets up the pace, and then proceeds to thunder down the rails with no sign of stopping. Then it suddenly hits the brakes and grinds to a halt with an evil screech.
Possibly my favourite part of Moonchild (that nobody else seemed to mention) is the beautiful guitar line going off underneath the chorus.