In the name of promoting character variety:
1. Attributes - STR's benefits should be brought more in line with DEX's.
2. Race - PCs have all classes as favoured; won't eliminate the world's stereotypes but helps eliminate the PC stereotypes.
3. First level - Change the initial skill ranks to a fixed number (like 20) plus 4xINT Mod. plus one level of first level class. Or, some other method that doesn't encourage taking only a limited number of classes at first level.
4. Class - Major overhaul.
5. Feats - Major overhaul.
6. Weapon stats - Bring the true efficiencies of different close range combat styles into some semblance of balance.
One more shot at trying to explain the problem as I see it: The problem is that a lot of races, classes, feats, and combat styles just aren't worth using not because in absolute terms they are that awful but because in relative terms other options are so much more effective.
It's not a "Why did I build this character?" experience but a "Why didn't I build a different character who is going to be a lot like every other character?" one. As much as personality and experiences could result in differentiated characters, having the rules encourage cookiecutter characters is discouraging.
It's possible to come up with a campaign where the bardiche-wielding, 20 STR, cleaving barbarian is not a good choice. That's not the point. The point is that for most sets of options, one option is clearly superior to the other.
A first level dude with no feats and with a bardiche or greatsword and a 16 STR does 2d10+5 damage and APs most stuff. Add in some seasoning and you have a character who consistently forces massive damage saves. Thieves don't take very long to force them either, though there are times when sneak attack isn't usable. Really, the discrepancy between forcing a MDS and not is so ... uh ... massive that it's easy for someone without at least one of - 2H weapon, Power Attack, Sneak Attack - to be just taking up space in combat.
Sure, you can jump through hoops to try to be as effective (not just in combat) as another character who was built better, but that seems only appealing for people looking for a challenge. For instance, while one character is sinking two feats into being a combat powerhouse and can diversify from there, the character with half a dozen feats to be similarly combat useful doesn't have the ability to diversify and will remain behind the curve in some other area.
Combat is the most obvious place for comparison, but it's the same story elsewhere. Having a high INT out of the gate generates increasing benefits where WIS's, for instance, are static. A lot of noncombat feats effectively don't exist because no one in their right mind would take them because others are so much better.
Now, while trying to bring diversity into characters would be my focus, there's quite a list of individual changes I'd also like to see. I personally despise how codes of honour currently work as they are money for nothing, for instance.
I actually don't have much of an opinion on defensive blast. It seems horribly wrong, but I want to playtest a scholar first or, at least, see enough antagonist scholar abuses of it. I would say that one of the less obvious benefits of it is that it give a real purpose to ranged combat.
And, much like I prefer options in character archetypes, having more options in spells would be more fun - again, diversity.