So you want to develop an RPG?
When developing a more complex game type such-as RPG, what you have to do is actually figure out alot of things before you do anything.
Mainly,
What does RPG mean to you?
There are just so many types of RPG, it is very hard to simply come up with a point-by-point guide for development.
Here are the general types:
Japanese RPGs, are generally deep story driven games that rely on you having no/limited control over your Statistics Development however provide you with a very indepth overview of your Skill Development. The battle systems are usually presented in a Turn/Time Based Fashion, providing you with a more strategic battle style.
[Games available in this style: Yu-gi-oh, Pokémon, Final Fantasy, Grandia, and Fantasy Kingdom]
Traditional RPGs (D&D), often have very loose storylines, relying far more on giving you more control over your Statistics and Weaponry Selection. Providing you with more of a Character experience rather than a Story experience.
Battling in these usually ends up being a case of point'n'click, so you generally click on an enemy you wish to attack.. it is all real time.
[Games available in this style: Bauldur's Gate, Neverwinter Nights, Syndicate, and Icewind Dale]
Action RPGs, these are odd, because they can work with and without a story.. but generally with a loose one relying on you to solve puzzles. Fighting again is done real-time, but in a more hands on approach. You get little or no control over your Stats, Weapons, or Skills but they grow as you progress.
[Games available in this style: Final Fantasy Crystal Chronicles, Zelda, Starfox Adventures, Beyond Good & Evil, and Sphinx & the Cursed Mummy]
There is a fourth type of RPG that could argueable be closer to D&D than any of the official D&D games.. and that's Fallout.
It is a unique turn-based RPG that really is very traditional in the way it is presented.
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So when yuou think about it, the first order of business is deciding.. what variation of the RPG Genre you actually wish to create before anything else.