The division between Kill 'Em All and Ride The Lightning is huge.  The albums sound like two different bands.  Amazing.  Where KEA was juvenile and garage-bandish, Ride The Lightning was the polished effort.  Don't get me wrong, a lot of great songs came from KEA, but Ride The Lightning is better.  Fight Fire With Fire opens up the album (back when it was an actual album) and never looks back!  Absolute pure shred!  Ride The Lightning, Creeping Death, Fade To Black, & For Whom The Bell Tolls!  All Classics!  Their first really professional effort for Electra, with the final batch of Dave Mustaine co-written tunes. Clearly one of the greatest metal albums of all time.