As seen in the trailer, most of the original features are intact, while I do see a couple of new features (or they were added after I stopped playing the original). With the basic classes and 1 advancement thus far, Ragnarok Online: Prequel has just ended its first test last month.
The dungeon system here is somewhat similar to games such as Dungeon Fighter’s and Dragon Nest’s, with a couple of difficulty levels. The monster cards are still there as well, thought it follows RO 2′s system where they are equipped on to characters rather than gears.
Source: MMOCulture