Several of these rank among THE definitive Halloween episodes - not just of cartoons, and not just of the 90's, but of any kind of show, ever. Period.
The first five or so installments of the traditional THH are classic episodes that were among the highlights of the seasons - and seasons 2-6 were nothing to shake at stick at to begin with. There's no point in doing long recaps here - I'd ramble on all night. I'll just pick my favorite scene of them all: the one in which Burns puts a brain on his head and says "look at me! I'm Davy Crocket!" This is one of the better Simpsons lines of all time, which is really saying something.
I forgot to set the VCR one year, and ended up missing the 6th installment - a fact that haunted me for the rest of the year. As it turns out, though, the sixth installment (the one with the giant advertising characters coming to life) marked the beginning of a definite change - around this time, THH went from being the highlight of the year to being, sometimes, the low point. It's been hit or miss since then, but, alas, mostly miss. It's only natural that once you get up to nearly 20 annual specials, with three stories each, you'll start to run thin on ideas. There are only so many twilight zone episodes that one can parody, after all. When it scores, though, it scores, and it's gotten better the last few years.
Still, THH 1-5 should be in EVERY collection of Halloween Specials, and none should really be without the others, either, if only for the sake of completism.