First observation: no character generation rules, just five sample pregenerated characters.
Rateliff's Rule #1: Without character generation rules, it's not an rpg.
That's not a fatal flaw in this case, since this isn't an rpg: it's a playtest document. It's more akin to a crash test dummies car, as opposed to a roadster or sportscar, something you cd actually drive: i.e., designed to find out how certain things will happen in certain circumstances and make adjustments accordingly.
That said, haven't gotten too far in the rules yet, but there's a lot to like here. The characters provided come from the four traditional D&D classes: Cleric, Fighter, Wizard (e.g. Magic-User), and "Rogue" (as they're still calling the Thief)-- and four traditional races: human, dwarf, elf, and halfling.* The six traditional ability stats are all here, and used for more or less traditional applications.**
Two new things so far:
(1) Hit points now equal your Constitution score plus a die roll based on yr character class: d8 (Cleric), d12 (Fighter; an inflation from the traditional d10), d4 (Wizard), and d6 (Thief).
Based on the pregen characters, they've assigned a default value of half for each 'die roll' (e.g., the Fighter has Con 14, a d12, and 17 hp [14+ (0.5x12)=17]), but to their credit the rules are firm on rolling for hp rather than assigning a maximum or average, with a reasonable back-up rule in case you roll really badly. They deserve a thumb's up for that.
So, these rules preserve the long tradition of hit point inflation from edition to edition, but in a whole new and rather interesting way. Don't know if I like it yet --the end result looks to be that characters basically start out at the equivalent of third level so far as hit points go yet with essentially first level abilities -- but they're to be praised for restoring a random element in 1st level hit point generation, which reduces the sameness of too many characters being too much alike in stats.
Rateliff's Rule #2: Randomness makes for a better game; predictability for a diminished one.
(2) the 'Advantage/Disadvantage' rule is new, so far as I can tell (if there was something like this in 4e I certainly missed it). It's another interesting idea, but completely unlike D&D. So, better than the myriad bonuses and penalties that have plagued the system since shortly after 3e debuted, but not quite in keeping with the 'look and feel' of D&D tradition; have to see if its utility overcomes that. I suspect in my own game I'd just drop the advantage/disadvantage rule altogether and leave it up to DM discretion.
Finally, perhaps the best sign of all is the adventure they've provided for the playtest: THE CAVES OF CHAOS, the dungeon-delving section of B2. KEEP ON THE BORDERLAND. This represents a nod to shared experience, since more people have played this adventure than any other D&D adventure ever published: the quintessential dungeon crawl with a workable dungeon ecology and rationale to go with it. I got to write the sequel adventure (RETURN TO KEEP ON THE BORDERLAND) as part of the 'Silver Anniversary' series back in '99, so it's a setting that I have a particular interest in.
Now if I cd only find a gaming group to playtest with (both the groups I signed up with petered out back in February): I already have some wicked ideas of things to throw at them.
current reading: D&D NEXT Playtest Rules
*as opposed to, say, the furries with tails and horns that had come to dominate the player character races section of the D&D PH.
**though I'd shift things like jumping a chasm from Str. to Dex.; perhaps less realistic but seems a better intuitive fit (as it stands, the big burly fighter can make that leap but the nimble acrobatic thief cannot).