I've been on a hiatus from d20 for a considerable length of time. Have played Savage Worlds, Iron Kingdoms, and Rifts (don't ask) in the meantime. This has given me a lot more perspective and ideas on mechanics that I feel work well and don't work well. (Note to self: the concept of the wild die is awesome and needs to be brought over to d20.) I'm reading about Dungeon World with great interest. Now I've missed out on a bunch of things with D&D 5e, and I have zero clues about what's going on with the game.
Would anyone be so kind as to bring me up to speed?
Rather than download the packet and start reading, I would suggest you to read through a few articles in the Legends & Lore blog by Mike Mearls, because it will be quicker and will illustrate the bigger picture.
http://wizards.com/DnD/Article.aspx?x=dnd/4ll/20130107
http://wizards.com/DnD/Article.aspx?x=dnd/4ll/20130114
http://wizards.com/DnD/Article.aspx?x=dnd/4ll/20130122
http://wizards.com/DnD/Article.aspx?x=dnd/4ll/20130128
http://wizards.com/DnD/Article.aspx?x=dnd/4ll/20130422
Overall I would describe (very roughly!) the current status of 5e by telling you to start imagining it as 3e being modified with the following points:
- simplified combat rules (much simpler action economy, small list of possible actions, circumstance bonuses replaced by advantage/disadvantage), on top of which you'll be able to add
rules modules (unreleased yet) if you want more combat complexity
- bounded accuracy, i.e. all level-based bonuses in the game much more limited than in any previous editions (think that in most cases +5 will be the max you get), much less sources of bonuses available in the game; the game focuses more on narrative improvisation than on stacking bonuses
- character complexity available in 3 tiers called "Basic", "Standard" and "Advanced", meaning that each player can choose to play the same character concept using a simple (mostly predefined) "bundle", or select her character features using a series of smaller packages (such as Backgrounds, Specialties and subclasses), or cherry-picking the details, but whatever the player's choice, everybody should end up with characters balanced with each other thus all playable at the same table
- similar complexity tiers exist for group rules; within a Basic setup, emphasis is on narrative improvisation, while the emphasis shifts to relying more on detailed rules as you add modules to increase complexity
- the system of variable complexity for both the characters and the group's rules ("modules" and "dials") makes the game more like a toolbox for each group to find their favorite setup
- all traditional D&D classes, races, monsters and spells (with some exceptions to the latter, but think we haven't see them all yet) are in, emphasis is currently on legacy rather than adding new, unprecedented stuff
- the game doesn't make assumptions on wealth by level, so that magic items are supposedly entirely optional (they tend to grant additional abilities rather than bonuses, thus they should never end up being "must-have")
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And if you want to know about more specific parts of the game for the player:
- Standard character creation implies to choose Class & Subclass, Race & Subrace, Background, and Specialty (or pick feats individually), plus lesser details (equipment, some classes' spells or special abilities); Basic character creation (unreleased yet) presumably handwaves Subclass and Subrace choice by giving a default, and gives you ability score bonuses instead of feats
- all classes have subclasses (except for Fighter and Barbarian currently but will have them too) also called "choice points", which alter the base class by granting a package of features which can shift the focus of the base class (e.g. make a Druid rely more on spells VS rely more on wildshape, make a Cleric know extra spells otherwise unavailable VS granting better armor and weapon proficiencies)
- backgrounds (currently under re-design) are supposed to represent what your character is when not adventuring (if your campaign has downtime) or what she was before adventuring (if you don't have downtime), and grant stuff useful during downtime
- specialties (currently under re-design) are feat chains or feat pools; the DM can make all the feats available individually or can allow some feats only through specialties to represent prestige classes with restricted access; feats (currently under re-design) will be much bigger than in 3e
- skills (currently under re-design) will become optional on a group basis; if you group doesn't use them, focus is simply on ability scores check
- spells won't stack nearly as easily as in 3e thanks to the concentration rules (i.e. only one spell requiring concentration can be kept active at a time, although not all spells require concentration)
- spells don't scale with caster level but scale only if you prepare them in a higher level slot
- spellcasters are not fully vancian, they all prepare a number of spells per day, but then they can use their daily slots to cast any combination of the prepared spells
- cantrips are at-will
- main spellcaster classes can cast spells as rituals, i.e. taking a longer time (never usable in combat) in exchange for not using a spell slot
- classes who are capable in combat generally deal significantly more damage than in 3e, e.g. every bunch of levels the basic weapon damage gets a multiplier
