DnD Next is running an open playtest for anyone who wants to test it out. I downloaded all of the files and took a look at them though I didn't actually play through the adventure supplied; it looked like a very large time investment just to learn all the ins and outs of the adventure prior to even starting to run fights. Rather than a more modern adventure that is segmented into discrete fights that are all reasonable challenges the module they supplied is more of a 'realistic' module in that there are plenty of utterly trivial fights and plenty of fights that will wipe the party out for certain. It is meant to be a complex world that the players can interact with by ambushing people, making groups work against one another, and other such tricks rather than simply by fighting. I like that a lot actually, though it works far better for a group interested in roleplaying than playing a board game.
It appears as though this is the direction Wizards is going with the entire design of Next. They have gotten away from a grid system, zones of control, and attacks of opportunity and instead simply let people move anywhere they want on their turn. Rather than move actions, swift actions and standard actions each character may move and take an action on their turn. Shifting and 5 foot steps are things of the past and it seems like it would be possible to run a fight in Next quite easily on a model with no measurements on it at all - eyeballing the ranges and movement should be quite possible since precise positioning is no longer key. This is going to make the game a lot more fun for roleplaying oriented gamers I suspect since calculating out the best possible turn is going to be very easy and combats should be much less mathy. There will be no more searching through stacks of ability cards and trying to calculate the best use of each of the three action types like in 4th edition.
There are some things I really question in Next though. Chiefly among those is the return to rolling for hit points. The way Constitution affects this is that you roll a die for hp which ranges from a d4 at the lowest to a d12 at the highest and if you roll below your Con modifier you get to take your Con modifier instead. So in this way Con is useful for people with crappy Hit Dice and pretty much garbage for people with good Hit Dice. I don't much like this whole concept at all and I would definitely scrap it in exchange for fixed HP / level. Con already gives you a little bit of HP in that you get HP equal to your Con mod baseline and it helps you heal faster - it actually doesn't need to give you more than that to be good.
One other questionable decision is setting up the game to be a single stat game just like 4th edition. Every class bases their attack roll and damage roll on a single stat, which is good in that stats seem to help each class comparably, but classes that use Dex to attack also get their main stat adding to the armour class. When a single stat determines all of your offense and most of your defence it is not going to leave much room for innovation in character design. Other than that though I really like that the stats are all useful defensively, if only in minor ways, and that casters' damage actually scales with their stat in the same way that thugs' damage does with theirs.
Something that many people are complaining about is that there is a serious return to casters having options and thugs having only 'I attack'. I think for some players 4th edition gave people too many choices but only having 'I move here and attack' in combat is very dull. We haven't seen a list of feats yet though nor do we have any real sense of what other options thugs might have. In the sample character sheet there is virtually nothing for thugs to do aside from attack but that really might change once we know more. I will reserve judgement until we see how it plays out but I do hope they find some kind of middle ground where thugs have a few different options to use without going as far as 4th did. Not that I minded 4th myself but I know lots of people who want a mechanics lite game and Next seems likely to deliver that.