- The advantage/disadvantage mechanic is excellent. I love that, whether making skill checks, saving throws, or attack rolls, the means of adjusting the odds remain the same. It reminds me of the guidelines given in B/X that suggest an attack roll penalty or percentile roll for unusual tasks, except that here the DM doesn't have to take any time to think about just how likely it is that, say, a character will be able to swing on the chandelier.
- The inspiration mechanic follows on from this, and I think it's a good idea. At first, I thought it might get confusing or too mechanical, but it's as simple as can be: when you use inspiration, you get advantage. Being able to give it to other players is also helpful, especially if one person keeps rolling threes or fours.
- The subraces for demihumans are good, managing to ensure a variety of characteristics and abilities even among characters who might have the same race and class - a bonus, since the Basic Rules only contain the "core four" races (dwarf, elf, halfling, human) and classes (cleric, fighter, rogue, wizard). Ditto for the character backgrounds.
- Attacks of opportunity have been made even simpler. In 3.5e and Pathfinder, there's a whole table of different Move, Minor, and Standard actions, telling you whether each one provokes an attack of opportunity. One of the few changes that 4e made that I genuinely like was simplifying this, to the point where only two actions provoke an opportunity attack: moving, and making a ranged or area attack. (It still baffles me that Pathfinder didn't use the looseness of the d20 System to incorporate this change; maybe they will if a second edition comes around.) Now, in the 5e Basic Rules, it's only moving that draws an opportunity attack. Making a ranged attack while threatened by an adjacent enemy instead gives a penalty on the attack roll, which is fine.
- The necessity of the dreaded Grid has been removed, although there is a sidebar giving optional rules as such. This was the thing that pissed me off about 4e; giving distance only in squares destroyed whatever shred of immersion might have been left after the way that everything was divided into "powers". If I ever play this, I'm thinking I'll use a mat and minis, but not lock the combatants into the squares.
- The default modern method for ability scores - 4d6, drop lowest, arrange to taste - is given here, along with a set of (for this range) average pre-picked numbers. If I were to DM this, I would probably have everyone roll 3d6 and arrange to taste, instead; there are enough ability score bonuses given by race (and increases every other level or so) that there wouldn't be too many below-average scores.
- The one criticism I have is that there is only one cleric Divine Domain and one wizard Arcane Tradition. While these categories are pretty broad, it seems kind of silly to explain all the details of Domains and Traditions, and then only give the player one possible choice - telling them to buy the PHB if they want more. A couple of extras (such as the three gods and three schools given in the Pathfinder Beginner Box) would have gone a long way toward creating some more variety between the classes. The same criticism could be leveled against the similar systems for fighters and rogues, but the ones given there are broad enough to encompass pretty much anything a player would want to do with those classes.
(Side note: the DM screen available at my local Barnes & Noble is four-panel landscape. Nice!)