I place it *juuuuuuust* below ALIENS, personally. But it's close.
They're both better by a decent margin than anything else he's done, though. I dont' think he's ever made a bad movie. Or even really one you could call "mediocre." But after those two, his technical prowess consistently improved, but the quality of his films never quite got back to that 1986 level.
Meanwhile, look at Miller's filmography:
The Mad Max Trilogy
The Witches of Eastwick
Lorenzo's Oil
Babe: Pig in the City
Happy Feet 1 & 2
Fury Road.
That's kinda crazy. Now, Thunderdome (not all him) Happy Feet Two (not all him) and Lorenzo's Oil (all him) are wavering around that mediocre level, but there are a lot of bonafide successes in there. And they're all, at the least, very visually interesting. He's doing stuff with his imagery that not a lot of directors do. There's something about the way he sees things that is just markedly different from a lot of people, in a way that isn't very easily replicated at all.