At this point I'm sure that I'm boring non-D&D gamers to tears with all of this, and we're getting into some minutiae at this point so I'll just lump all the other important playtest material into one post.
Specialities (formerly "themes")
This is the second lens that helps define your character, along with Background. While your background focuses on your skill-set and some role-play based advantages your specialty is the stand-in for Feats and focuses entirely on mechanical benefits. Some specialties are fighting styles (such as Archer or Two-Weapon Fighter), while others are more like enhancers or minor multi-class bonuses (for instance anyone can be a Magic-User, it grants non-wizards a small number of cantrips while it expands the wizard's spell repertoire a bit). Since we're only allowed to see the 1st and 3rd level feats in the playtest it's hard to see how they'll play out long-term but it's clear that a character's class is a lot more important than their specialty. The benefits a Sharpshooting Fighter gets are still much stronger than any other class with the Archer Specialty, although of course the Sharpshooter will certainly want to consider the Archer specialty.
Specialty's are pretty decent, they're focused primarily on providing clear cut "paths" characters can take with their abilities rather than the endlessly branching feat trees of older editions. That way you don't have to spend time optimizing and synergizing and just pick a theme you like and go and limits the chance for newbie traps. That said, specialties are not nearly as universal as Backgrounds. For instance, if you're the above Sharpshooting Fighter then you're practically obligated to pick up the Archer specialty. Hopefully that loosens up a bit when more Specialties are introduced. The Necromancer specialty is especially neat, a new way to handle the specialist wizard (although it's 3rd level ability to animate a single skeletal servant will become quickly useless at higher levels, hopefully later feats help it out).
The spells introduce us to how magic works in the new edition as well as a taste of how wizards will work. Most of the spells are pretty familiar and while they no longer seem to scale damage with level they're still all working more or less how you expect them to. Damage for "focused" spells is significantly higher (melf's acid arrow has a base damage of 4d8 for instance, the third level Inflict Serious Wounds does 8d8). There are two big changes however:
The first is the inclusion of "ritual" versions of spells, basically longer and costlier (in terms of material components) versions of normal spell which can be cast without preparation. It's a neat idea, and one that makes it easier for spellcasters to prepare their spells without having to worry as much about things like keeping the campsite secure or being ready to remove disease or blindness.
The other big change is that many spells have different effects based on the target's hit points, most notably enchantments and other mind affecting spells. For instance, Charm Person only allows a saving throw if the target has 25 hit points or more, creatures with more than 40 hit points are immune to Bane and so on. Now, I can definitely see why these changes were made, but it has some effects I don't think the creator's accounted for.
For example, due to their low hp totals and the fact that this edition doesn't grant class-based saving throw bonuses it means that wizards are the most easily affected by mind-control and other magic, while fighters and clerics are about tied as "most resistant". For example, a 3rd level fighter with Con of 14 would have an average of 30 hit points, giving them a save against Charm Person...a 3rd level wizard would have an average of 15 or less and would have to make a save. And since arcane spellcasting doesn't demand Wisdom they don't have great odds. Ironically this means wizards will likely duel one another with mind control before anything else. It seems like basing this off Hit Dice rather than maximum hit points would be more logical and fair.
Equipment will also be fairly familiar to long-time D&D players. Armor works very similar to 2nd edition...all armor, no matter how light, prevents magic-use and characters basically become unplayable when strapped into any non-proficient armor. It's a dumb rule...but at the same time I can see why they wanted to ditch the fiddly stuff like arcane spell-failure chances. So in the end I guess I don't care. They seem to have dealt with the issue that meant heavy armor is functionally less useful than lighter armor, so that's good, but this is forcing some ridiculous pricing decisions. For example, scale mail being 6 times the cost of chainmail.
Weapons are likewise similar but simplified. For instance range increments have been ditched, there's just a short range and a long range which is four times the short. However, they've definitely gone overboard with the weapon classes. The division between simple, finesse, martial and heavy, aside from over-complicating things, makes for some ridiculous situations. For example, a cleric can use a spear or mace (simple weapons) but not a staff (finesse) or morningstar (martial). In fact, the war domain gives clerics access to martial weapons so you have someone who knows how to fight with a longsword, flail, warhammer, battleaxe, trident, handaxe or war-pick...but not how to use a dagger. A rogue can use a katana or spiked chain but wouldn't know how to use a longsword. There's really no reason why Finesse weapons need to have their own category when they could simply be a Property of the weapon like being Two Handed or having Reach.
I've only skimmed monsters but I'm definitely seeing a move back towards 3rd edition style monsters and away from 2e (they behave more like PCs than a separate type of character) or 4e (lots of weird, unique situational abilities). I'm kind of sad to see some of the weirder abilities go and be replaced by class levels...but ultimately it's an easier way for people to build and balance their own critters so I'll accept it as a necessary evil. So far it really seems to be six of one, half a dozen of the other. Some monsters are clearly just PCs in weird suits...others are more unique. Too soon to say really.
One 4e feature that is showing up is in the style of encounter building, creatures are given "elite" or "solo" classifications to give an idea of how they should be slotted into encounters. Whether this will do any good remains to be seen...there's a reason why the vast majority of non-d20 RPGs don't bother much with things like challenge ratings. Notably the hit points of monsters have been drastically cut for the tougher ones, probably a good idea.
Well, I've more or less looked through the whole thing and I'd have to say I'm still feeling fairly positive towards the new editions. There are a lot of places I can see things that look wobbly or incomplete but it is a playtest so I'm willing to have faith that many of these issues will be corrected. The changes between the last playtest and now show that they're at least open to the idea of change...here's hoping it'll all be good changes.