This stuff is in no particular order.
1. In general, I really like the way that D&D Next has come together. There's a good balance of the simple and the complicated here, and it's not immediately clear that the more complicated options are going to work "better" in the game than the simple ones do. For example, at fourth level, you have the option of taking either a +2 to a single ability score, +1 to two ability scores, or a feat. Now, the feats are undoubtedly the more complicated, more evocative choice, but does that make them better or more powerful in the game? Probably not.
2. Along similar lines, one of the things that I loved about D&D's Fourth Edition (4e) was the way that it balanced the game at all levels. For the first ten levels, you were supposed to be a locally famous hero, helping to keep your town or city safe. By the time you reached 11th level, you were regionally famous, working with kings to help shape the fate of nations. And eventually you reached the Epic Tier, moving in the same circles as the very gods themselves, helping to shape reality across the many planes of the multiverse. At every level, the game was balanced, providing enemies and statistics to support pretty much whatever kind of game you wanted to play.
The problem with that, though, was that over time, you gained so many different kinds of powers, area-effect abilites, and action-interrupts that the game's action economy eventually broke down. And that made running the game at those higher levels really, really complicated. It was a shame because the game itself had a lot of really interesting stuff at those higher levels, and I personally like telling those epic kind of stories, but the mechanics of the game itself at those levels were really, really hard to use.
So. D&D Next is simpler to use than was 4e, but as of yet, Wizards of the Coast (WotC) hasn't released even half as much support for those higher levels of play. True, we have some support for levels eleven to twenty, but as of yet there aren't any Paragon Paths or Prestige Classes, and no one has so much as mentioned adventuring beyond Level 20. WotC has said that they may include some Prestige Classes in the new edition at some point, but they're not in there yet, and if they're coming, we the fans haven't yet seen any part of what they're going to look like.
I personally think that Paragon and Epic Level play will probably be supported at some point in the future, but it doesn't seem likely those super-high level styles will be included in Next's initial release. Now, maybe that's good in that it will give the new edition room to grow vertically, but for me personally, I'd like to see what these guys are thinking.
3. D&D Next manages resources differently than did any of the other, previous editions. Even "short" rests require resting in place for a full hour, and even then, they provide minimal benefits compared to full, eight-hour rests. What's interesting about that is that it makes the game flow differently than previous editions. In early editions of D&D, you basically saved as much ammunition as you could, buffed your party to the max before the big battle, and then went in and kicked ass. 4e was a little different because it was very so carefully balanced, but the downside of that was that every fight became an entire war in microcosm. This ultimately slowed the game, and that wasnt good.
Now Next brings back this idea that not every fight needs to be the Battle of Gettysburg, and that's good, but it also adds in a whole element of resource management, wherein you may have to manage hit points and other healing resources over the course of an entire dungeon crawl rather than just from day-to-day or from Long Rest-to-Long Rest. I suspect that this will make the process of planning and running games a little more interesting for Dungeon Masters (DMs) so long as they (we) can come up with ways to keep our Player-Characters (PCs) from getting eight hours of consecutive rest over the course of an extended expedition.
4. There's a lot more going on with the new multiclassing rules than I'd expected. For one thing, WotC (re)introduced ability score minimums for specific multiclass combinations. That's okay, but I wish that they would have made the minimums just a little lower. For example, if you want to take levels of Fighter or Mage for your second class, you have to have a minimum of 15 in Strength or Intelligence, respectively, and that's tough. 15 is a lot for a stat that's your second-best thing. On the other hand, it's not nearly as difficult to come up with a 14, and speaking objectively, I still think that folks with a 14 in something would have substantial aptitude for whatever that thing is.
5. Along similar lines, there's still no real support for a fighter/mage or close-combat mage in the Playtest. True, you can now multiclass to be a Fighter/Mage, but there aren't many spells or abilities that would make such a choice worthwhile. On the other hand, the way the multiclass rules are written, you can build a Hell of a powerful Cleric/Mage or Cleric/Paladin or something like that.
Basically, if you combine two spell casting classes, you're in good shape. If you try to combine two classes that seemingly have little in common, it looks like you'll have a harder time making it work.
6. It was nice to see that this last packet (finally) included some "exotic" races. Specifically, we have Tieflings, Drow, Warforged, Kinder, and Dragonborn. I'll admit that I was expecting some support for Tieflings, as I've mentioned here before, but I was surprised to see Drow and Dragonborn supported and very surprised to see support for the Warforged and Kinder. I guess that means that WotC is fully committed to supporting a bunch of different campaign settings. No problems there.
7. Finally, this packet included a Bard class. Nice design there. The Bard has a lot of control-type powers, powers that let him/her affect the battlefield either by buffing allies or hindering enemies. But the Bard still has to actually fight with a weapon in order to hurt the bad guys, and that's good. I mean, it's fine to have a Bard that can use magic, but the Bard is supposed to be the guy who can do a little of everything, and that means that he has to have a reason to use his weapons occasionally.
And that's all I've got. What did I miss?