Things like Swordmage sort of show they understood some of the core problems themselves, quite quickly too. But the core books, it's not here.
Whatever passed for playtesting didn't get into the core books at all as far as I can tell, other than perhaps some tweaks on the number of healing surges per class, or getting a power to fit the formatting properly.
Character Races
So they don't really fit to the stats the classes need, at least not as well as the monster manual races for most, but here they are in all one and half pages plus art each, and the MM races don't get racial feats.
Dragonborn appeared in 3.5 Races of the Dragon, because those books all had three races described in them. It was fluffed as a replacement race where Bahamut transformed Elves and Dwarfs and such into this +Con/-Dex guy who had scales and was very angry about evil dragons (which is who Bahamat "gifts" this to).
Here they're an ancient lost empire (from before the current lost empire, turtles etc.) and are and all Paladins or Warlords. +Str, +Cha, and a feat for more damage. It implies the designers replaced the Str/Dex Half-Orc with this specifically to have a Paladin race, thereby displacing Dwarves and Humans from the role. Which, ... hmm. The lack of flexibility on the races is quite a problem all around.
They get a 1d6+Con damage breath weapon, which, they don't have Con, so ..., it's a Minion clearer. Note that a lot of people like Dragonborn, for the fluff you see, which, well, they are after all effective at a couple of useful character builds, which does help the fluff go down well.
Dwarf ... yes, they tell you to be Clerics, Fighters, and Paladins. Sort of a passible melee Cleric, but you shouldn't really be a melee Cleric anyway. They get a bunch of little tanky bonuses, but in core tanking is disfunctional.
There's the stupidest upgrade for Str(Con) fighters in the first splat, basically makes them immune to damage, which, uh, got nerfed quick enough, but if you're playing without nerf errata you end up with ... Binwin sort of working.
In core if you hit Binwin he totally just dies. Dwarfs suck in this, worst race. Like, there's a damage and AC feats for them, but they can't hit anything.
Eladrin used to be a type of Celestial of course, here's it's just elves from the future or something.
They are +Dex, +Int, and a damage feat. Best wand Wizard, but eh. They can Fey Step as an Encounter power, which people fussed over early on, but it's mostly an anti-grab thing, or for if something immobilises you in lava. Because if there's a lava square, that's coming, and you just save it for that. 4e, things are predictable.
Elf are sort of a wood elf here, which I find to be a strange design choice when the Eladrin are supposed to be the Fey ones, but like, whatever. I mean, make the Eladrin the wood elf and the Elf the high/grey elf, surely. But no.
These have +Dex, +Wis, an encounter attack Reroll, which is quite good really, because you can reroll your best Daily or Encounter power that misses, and there's a feat to make it work better, and move to let you move faster and still shoot.
So you're an Archer-Ranger, or you're not bothering. Which is a useful thing to be.
Half-Elf are +Con, +Cha, which is pretty useless outside the worst Warlock build, and you get some other class's At-Will as an extra encounter power, which, there's not really anything in core to cheese that out. There's stuff to give tiny bonus to allies, like +1 Perception and a +1 Initiative feat. Meh.
Basically, you're getting Con instead of Str on any Charisma build, and there's almost nothing wants that. I mean, it's better than Dwarfs because you're failing at using better classes.
Halfling get a fucking interrupt as an encounter power, forcing a reroll after an attack hits you, but before you see the damage. That's such bad game design. They also get +Dex, +Cha, and are thus your party Rogue (who are forced to use small weapons anyway). Being a Rogue is good, so being a Halfing is good.
Their feats make the interrupt work better, and give them an AC bonus, and let them move through large creatures without taking AoO. Which is all useful for Rogues. Like, this seems like what they meant to do with races, it's just that most don't do it.
They're 4' tall and just as fast as a human, which is because 3e made Halflings skinny instead of fat, which made them too light, so 4e made them taller so they could be as heavy as the AD&D ones.
Human only get +2 to a single ability score of their choice. This is fine in core because lots of class builds lack a useful pair of stats even considering the monster manual, things like lazer Clerics and orb Wizards and Warlords that want to hit things. They get feats to buff their action point action, and a save feat that everyone gets a better version of later.
Three years on every stat pair is supported by 2-3 races, and Humans are a bit shit.
Tiefling seem to be a late development Gnome replacement, having the same +Int, +Cha pair, that doesn't bear any relationship to their former stat bonuses. Again, at some point, they bought a specific race in to be a better flavour match for a couple of their classes, the shouty Warlord and tricky Warlock, but, ... it's just sort of, why is any of that stuff here at all?
Warlord isn't greatly different to a Bard even in concept, sword things and boost allies. Warlock could be a Beguiler doing the exact same things, and then both work conceptually with the Gnome. The changes are basically pointless a lot of the time, it didn't change the outcome, it was just different, even with
Gnome Tieflings.
Mechanically the Tiefling get +1/+Cha as an encounter power, and +1 to hit bloodied foes always, which is useful, hitting things more is good. The feats are more of that, hit and damage, though partly over-written by the math fixes later.
Again, some of them work. The Halfling, the Tiefling, they line up the stats and their powers and feats help do what the usual class is doing. I imagine that was one developer, and stuff like the Half-Elf and Dwarf were a different developer. Someone got it, and someone didn't.
So the useful core races are Dragonborn Warlord, Eladrin Warlord, Elf Ranger, Halfling Rogue, Tiefling Warlord, and maybe drop a Human on anything else if you're avoiding the Monster Manual, which, you might use a Cleric, Dragonborn Paladins happened, or ....
Classes start next, a lot of them aren't good here. There's a lot of 3e Monk in this, start bad and get worse, and there's also stuff just combines extremely well, sometimes while looking quite innocent. It did take people at least a little while to understand how it all worked under the atrocious power formatting.
I think I'll cover the classes by roles, because obviously some of them stand out as much better at the role than the other, and you can just do a whole party of one role, which they never even tested. I also have a huge rant about defenders wanting to come out.
PC, SJW, anti-fascist, not being a dick, or working on it, he/him.