Safe As Milk would qualify. While it's nowhere near the experimentation he would pioneer in later albums, it's still got some good music in the form of "Zig Zag Wanderer", "Dropout Boogie", "Electricity", and "Abba Zabba"
Probably any fan of any artist would say 'all of it', but almost every album Beefheart made was filled with completely original and wonderful songs that drew rave reviews and critical acclaim; all except his two 'Tragic Band' albums, which still have one or two good songs...
High Octane Nightmare Fuel: Some of the songs he did were just downright creepy. "Trust Us" has whispers of the title while Vliet bellows Let the dying die and let the lying lie.
"Well" and "Dachau Blues", both from Trout Mask, are filled with lyrics about death and destruction, the former conjuring up images of crows and bugs devouring the dead and the dying. "Bills Corpse" from the album is ostensibly about a dead goldfish but was apparently intended to make band member Bill Harkleroad feel uncomfortable.
"Autumn's Child" qualifies for this too -- a very haunting ending for an otherwise (mostly) accessible album.
Love It or Hate It: Pretty much the standard reaction to any of his music.