Since there's a lot of confusion going around, here's what the 1999 Hunter X Hunter anime did:
* It greatly expanded the Hunter Exam, including straight up adding another round after the tower round, which was pretty good for expanding characters from the forest round.
* The new anime skipped part of the cooking round. The 1999 anime kept everything in the manga from there, but also added a bit.
* The 1999 anime added bits to the Zoldyck, Heaven's Arena, and Yorknew arc.
* It skipped the Kastro vs. Hisoka fight.
* It greatly condensed the arc after Yorknew, due to the TV anime ending and having to cover the arc in OVAs. It ended there.
* Up through the Yorknew arc, people generally consider the 1999 anime's music to be better. It also had more imaginative direction.