In approaching adapting Uresia for Classic D&D I resolved to attempt to maintain the simplicity of D&D while keeping the rich, multi-layered setting details of the original setting. This is reflected best in my design of new classes: I simply chopped up the abilities of core classes (using Erin D. Smale's Building the Perfect Class document to generate XP tables as inspiration). Thus, for example, the Elu Pirate has some thief abilities, but is also a competent fighter on par with clerics.
As I posted about before, my only big stumbling block so far has been how to approach magic; I am loathe to develop a whole new system. More thoughts to come.