The Inner Mounting Flame is still a pretty remarkable piece of work. I love McLaughlin's guitar tone here, Billy Cobham is incredible, and Jan Hammer's ring-modulated electric piano playing is great. "Meeting of the Spirits" is such a great way to kick things off and "The Dance of Maya" is still a mindfuck. And "Awakening", jeebus.
Birds of Fire is slicker and not quite as good as the debut -- some lightweight filler compositions alongside some of their best (title track, "Miles Beyond", "Sanctuary"). Between Nothingness and Eternity is weaker compositionally than the first two albums but on the intensity scale, DAAAAAAAAMN. I've listened to other guitar-fusion outfits and they seem to lack the bullshit-free musical approach of these guys. (e.g. Return to Forever)
I'm not crazy about the second incarnation of the group. Apocalypse just isn't very good. Visions of the Emerald Beyond is better if not on the level of the first three albums. Inner Worlds has some cringe-inducing music.
I haven't heard the 80s version.