From the introduction:
The goal of this book is to present to the player and judge the world of Gothic Earth - in terms of the new D&D game system so that the flavor of the Masque of the Red Death (MotRD) setting remains basically unchanged while updating the campaign for the new D&D rules.
These rules are designed for the ongoing Living Death Campaign, which is a tournament campaign. This campaign was already underway before the introduction of the new D&D. That fact influenced some of the choices made during the design process. If you wish to use these rules for a home campaign, you may wish to make a number of adjustments.
In general many things remain fairly similar to the original MotRD. Magic is still slow, unreliable and occasionally dangerous to use. It is still set in the late 19th Century and the Classes, Skills and Feats have been adjusted to reflect that time period. It is the game mechanics that define how these things work or expressed that has changed. Skills and Feats have replaced Non-Weapon Proficiencies. Instead of Kits we have a greatly expanded group of Character Classes and Prestige Classes.