I like FireLance's points, and the similar lessons I've learned from Iron Heroes. So...
- Balance per-encounter
- Incorporate swift and immediate action, to increase options in each combat round
- Include complicated resource mechanics (like tokens) to further increase options in combat, but only as an alternative to more simple play (e.g. including Iron Heroes tokens but only for some feat and talent chains)
- Reduce number of unique powers, allowing for easier gameplay
- Increase the applicability of (all) skills in combat, by providing clear and scaling bonuses and benefits to the use of, say, Knowledge or Jump.
- Provide rules for "Opponents" that make them easy to run and most effective, not universal rules that allow players to play opponents.
But also....
- Reduced book-keeping; perhaps replace hit points with a wounds system/condition track
- Remove non-d20 mechanics, like turn undead or miss chance
- Unite some skills, e.g. Perception, Athletics...
- Simplified skill-rank system to allow for easier character generation; especially avoid retroactive affects (if he changed his Intelligence at fourth level...)
- Avoid affects with complicated ramifications. Instead of lowering your Dex, have the poison impose a -2 to ranged attacks, defense, and initative. Insted of lowering your level, have Raise Dead impose a negative energy level.
- Avoid having lots and lots of bonus types to keep track of. This is difficult, but will definitely ease gameplay.
- Simplify the spells. I have no idea how, but the spells should not require you to open the PH for every single one.
- Make the character's supernatural powers be inherent, not tied up in magic items.
- Make the magic items provide more extreme supernatural powers, but at a cost and with a nice flavor. It's best to tie them to the character, a la Weapons of Legend or something.
- Provide a rational for demongraphics and leveling, as a non-obligatory standard. Follow this through with reasonable economics.
- Incorporate action points in the core rules, as a means to balance odd-ball dice rolls.
- Incorporate interesting social rules, like the "social combat" or "get actions points" rules of Dynasties & Demagouges.
- Reintroduce the Birthright setting, with a more coherent vision and metaphysics.
- Lose the "Standard Action" term. Call actions "Main", "Secondary", "Swift", "Immediate", and "Free". A person can do a single main action, a single secondary action, and a single swift action, and any number of swift actions in his turn.
