One of my friends called this "The Best Edition", which is the absolute truth. So much of this book is AD&D (1st) and 2nd edition, not only in the rules that are simplified and made to work better than ever, but in the way the rules themselves are laid out. Take character classes for instance - you get a brief intro, then the rules, then it gets fleshed out. Hard numbers that you need during character creation or gameplay are real easy to find.
Everything is broken down, not just for the noob, but the veteran player. It's well organized and easy to understand.
The artwork in this book is beautiful, a far cry from the old AD&D days (tho I miss some of the Erol Otis pictures and some of the other artists). With one glaring exception, the picture of the Halfling is just sadly distorted...but that one illustration is easy to overlook considering the lavish color art throughout the book.
The biggest change is that CHARTS ARE BACK! Remember all those charts from 1st and 2nd Edition? Well here they are: overall Level Advancement, a separate chart for each character class, even a fun Trinket chart! Charts make things easy, it's all the rules you need in one handy to look place that jumps off the page.
Character creation is in the beginning and it's easy. Unlike 3rd Edition (where we needed an entire game session to create characters for the group then work out everyone's Feats and Skills), it's a snap just like in the old days.
Skills are still there, but forget what you remember from 3rd Edition about needing separate skills for horseback riding, aerial riding, and whatever-other kind of riding - now it's all greatly simplified and lots of stuff is taken for granted and not given a skill at all. And skills are tied in to your Background, which is a separate chapter where you can pick where your character comes from (think pirate or street urchin). This provides a nice packet of skills to get you started.
Feats are there too, but not only are they optional, if your DM allows their use they fit right into the class level chart like a puzzle piece - every few levels each class gets to add +2 to their ability scores (it's there on the chart!), but if Feats are used then the player has the option of taking a Feat instead. And forget the awful chains of Feats you needed to get something cool like Two Weapon Fighting, now you just pick a feat and are done with it. A few Feats DO have prerequisites, usually they are ability scores and in just a few cases they are other Feats.
All the standard races that you remember are here: Human, Dwarf, Elf, Half-Elf, Half-Orc, Halfling (aka Hobbit), Gnome, plus there's the Dragonborn (someone with Dragon in their family history) and Tiefling (someone with infernal [demon or devil] family history). Each is laid out nicely and all the main races have sub-races, such as Drow. Humans get the short end of this stick, we get a bunch of ethnicities from Forgotten Realms.
Character classes are where these rules really shine. All the classics are there: Fighter, Wizard, Cleric, Druid, Paladin, Ranger, Rogue, Monk. The Barbarian is back, as is the Bard, who's finally done right. The Sorcerer from 4th Edition is also back, basically a wizard who casts magic innately - he doesn't know as many spells, but doesn't need a spellbook. And there's a new class, the Warlock - a wizard who gets his spells from an otherworldly source (Fey, Infernal, or Great Old One - and yes, Cthulhu gets a mention here!)
Take the Paladin for instance, which in classic D&D was a holy warrior that had to be Lawful Good; while a great class that was powerful and also powerfully restricted in their requirements, it made for some cookie cutter characters. In this book the first thing you see is an illustration of a Half-Orc Paladin! They still are designed to fight in the cause of righteousness, but at 3rd level they choose one of three Sacred Oaths that defines what their character is and how it is played going forward:
Oath of Devotion - "The loftiest ideals of justice, virtue, and order." Basically your classic Paladin, though sometimes called White Knights, Cavaliers, or Holy Warriors (nice touch).
Oath of the Ancients - Known as Green Knights, Fey Knights, or Horned Knights, these seem designed for elves in that they serve the light and defend life.
Oath of Vengeance - Known as Avengers or Dark Knights...OK, yes, this is the 'Batman' of the D&D universe, but damn if this doesn't make me want to play a Paladin!
Almost all the classes follow this pattern - somewhere between 1st to 3rd level they pick a path and that defines them and some of the abilities they get as they level up. The exception is the Wizard, who picks a school of magic (remember those from 2nd Edition?) This system makes for an efficient way to create characters that are not just another Fighter, Wizard, Rogue, or Barbarian, but it does this without the overwhelming burden of Feats and Skills that smothered 3rd Edition.
The rules still have Saving Throws, though they've been simplified. Also the Ability Checks from 3rd Edition are here, but again they're streamlined and easy to use. Now we also have Advantage and Disadvantage - once you earn either, you roll TWO dice for your next hit/ability check, then take the highest (Advantage) or lowest (Disadvantage) of the two. A cute and easy way to work a lot of different stuff into the game without having a new rule for these situations...you get an Advantage or Disadvantage, done!
Finally I got to Chapter 9: Combat - this is where, after all the greatness that came in previous chapters, I fully expected the game to lose me. Not so! This chapter is - are you sitting down? - 10 pages long! That's it. It's just how a combat turn works, surprise, actions you can take, damage and healing. BAM! (make a save)
Where character classes and races make up the majority of the front half of the book, magic takes up most of the back half. Spells are laid out alphabetically, with large charts breaking down lists for each spell casting class in the front. Cantrips are back, most of the spell-using classes have them (Paladin and Ranger being the exceptions) and they are actually effective. Familiar names such as Mordenkainen and Otiluke have returned - I recall they vanished at some point. The descriptions are streamlined and nicely descriptive, sometimes there's also an 'At Higher Levels' bit at the end.
There are some useful Appendixes at the end:
Appendix A: Conditions - clear definitions of stuff like Blinded, Petrified, and Prone.
Appendix B: Gods of the Multiverse - Simple stats, geared mainly for Clerics, for divine beings from The Forgotten Realms, Greyhawk, Dragonlance, Ebberon, some of the Nonhuman deities, then the Celtic, Greek, Egyptian, and Norse pantheons.
Appendix C: Planes of Existence - This has been reworked slightly since AD&D, but it still makes sense. My favorite changes is The Far Realm, which lies beyond all the Inner and Outer Planes, and is where you're likely to find Azathoth and other Lovecraftian horrors.
Appendix D: Creature Statistics - Just enough to run some low level adventures, mostly wild animals though Skeletons and Zombies did make the cut.
Appendix E: Inspirational Reading - A favorite of mine from AD&D, this section set me to reading Moorcock and Lovecraft. The great classic fantasy artists are here, along with their modern contemporaries and some that I've never heard of.
The only downside is that this edition of the game took so long to come out. Long time players have had to suffer through 3rd Edition (which was a mess of Feats and Skills - I actually needed a 1 page cheat sheet to keep all the math in one place!), to an unplayable 4th Edition that was basically an online MMORPG on paper. I remain one of the only players of my old gaming group who still knows what their dice collection looks like.