A good question.
I think, it will be complete, when I feel it.
Completing the vintage Evil Warriors is the first goal for me. I like some obscure characters, like Gygor, Wun-Dar and the Green Goddess. Or characters like Geldor, the Wind Raider pilot or Oo-Larr. Collecting these, is also essential for me.
But there are also figures I won`t buy (all POP-characters, exept Bow and maybe She-Ra).
But I have to admit, that most of the figures I´ll buy, especially if I have a strong connection to them (Horde Trooper, Battle Ram vehicle, Sy Klone, Tung Lashor).