My only requisites for an alignment system are these:
1. Every alignment should be a viable game play choice (no dead end alignments). If good can conquer the world, evil should have the same capability.
2. There should be no 'pvp/non-pvp' alignments, so to speak.
3. No alignment should force a game mechanic induced alliance to everyone of the same alignment.
4. No alignment should be allowed to temporarily 'hide' inside another alignment.
Being a veteran of table top rpg, not to mention MUD and MUSH programming, I have seen many many many alignment systems come and go.
IMPO, the old D&D style system leaves me flat (admittedly upon occasion there's a fair interpretation of it that people generally 'live with'). I think it's very two dimensional and I would love to see something more dynamic, that allows players to make tough moral decisions in between the black and white extremes.
The problem as I see it is this.
Evil performs evil generally based on risk vs. reward.
Good performs good generally based on who they are. ie. If I'm playing a good char, I generally DO good regardless of reward, and sometimes regardless of risk (on principle).
So how do you make good base their decisions on risk vs. reward, and similarly evil to base their decisions on principle?
I've attached a text file describing an alignment system from the Palladium Universe that I really enjoyed as my table top rpg days were coming to an end. I would love to see something as full of choice and nuance as this system was for me (at least in comparison to the old D&D system). Just something to consider.