A lot like 4e, but even more streamlined. I really
dislike how basically your class/build hangs so important on a primary ability score, and that ability score needs to be huge. This makes multi-classing out of your primary score a pain in the ass, and gives huge incentive to play a race with the boost to that primary score, as well as having low stats except for your primary/secondary score or else "the maths" doesn't work.
No "Expertise" BS ever. Make "The math" work from day one.
Magical weapons aren't needed at all for "The Math" to work, therefore magical weapons can be made COOL, Unique, and Rare, rather than "+1 sword that does +d6 fire damage on a daily". I'd be happy if folks only had 1-3 magical items their entire career - and clung to them. Magical items are not in the economy.
Abstract the economy and integrate favors, boons, resources (Keeps et al) as part of it.
Tie combat powers/class features to the Combat Role, but create a separate Out of Combat Role and tie skills to that. Something like 'Scholar' 'Scout' 'Sneak' 'Socialite' 'Tough Guy' 'Athlete'. Each of these comes with a package of skills. This way, your Fighter is a Defender, but he can also be a Scholar (and have knowledge skills rather than physical ones), a Cleric can be a Sneak (stealthy and thiefy) and a Wizard can be a socialite (with social skills instead of knowledge).
Revitalize skill challenges; they don't go far enough. Instead, model them after combat, with various options. For instance social combat (whittling away resolve/putting conditions) instead of just "Bluff/intimidate/diplomacy vs. DC". Silo non-combat powers to the Out of Combat/Skill Role.
I almost want to see the system look like lego blocks; you can plug a piece in or leave it out, and it doesn't effect the Game. Such as a player picking a Class Feature package, a Combat Role, and Non-Combat Role. Leaving the economy out, leaving magical weapons out, or leaving COMBAT OUT is purely OK - you can assemble and run a game without one of the other parts.