Design philosophy idea: Focus on team play, not "my character can do everything yours can do." Return to specialists, not generalists. New classes in older editions were based on "well, what could exist in the D&D world?" which makes things a little more generic. If a rogue can do anything a monk can do, why play a monk?
Magic that adjusts ability scores aren't so fun, no-one wants to continually recalculate ability mods. "Gauntlets of Ogre Power" don’t grant you a +2 bonus to strength, for example, they’re about smashing and lifting, not a strength mod.
Dieties: Fewer gods, more hierarchical structures. Gods have powerful llieutenents called "exarcs." The once-god of Gnolls is probably an Exarc of Bane, God of Bad Stuff. Player characters can become exarcs, in time...
Magic Missile requires an attack roll, that's interesting…
Alignment: It's changing. "alignment isn't terribly important." No weapons that punish characters of a specific alignment. It's just for story color. It may define who you hang out with, but not what you can do. There's an "unaligned" option (most commoners have this one.) There's no Detect Alignment spells (YES!!!!) Paladins aren't Lawful Good anymore, though they DO have to follow their Deity's code of conduct (this is brilliant!!! Paladin is "Champion of the Faith," now.)
Skill points are too fiddly, "complexity where it’s not needed." Simplified – not a points system, just saying "these are bonuses because I'm better than most people” rather than working out points.
“all players get a few powers at first level, like wizards and clerics do, to help round out both powers and personality.” (I don’t see how these are different than feats…) A character with “brute strength” is probably different than someone that focused on tactical powers. No real change to stats, but include stat sets like a template. (point-based and template-based stats are emphasized over rolled, because rolled stats tend to create inequality…)
Dragonborn, dwarf, eladrin, elf (elves and eladrin are fey, now), half-elf, Halfling, human, tiefling (gnomes are in monster manual, though—as antagonistic semi-fey, with rules for playing as PC as an option).
Cleric, fighter, paladin, ranger, rogue, warlock, warlord, wizard (hmm, no sorcerer, no bard, no druid! Maybe you can customize to make one…)
Wizard is the only “controller class” in the initial PHB (more coming soon, though—sorcerers and psionics later on, possibly a divine controller with big AOEs…I don’t like the “mmporgification” of my table-tops…) Wizards are not as versatile in 4th ed, they’re not “swiss army knife” characters. Few self-boosting powers, endurance powers…with emphasis on class roles, wizards are more focused, less generalists (but “leaves us room to come back later on”). Clerics, too, lose a lot of generalism.
Classes have “builds” (flavors of the class that lets you customize, differentiate characters if there’s duplication within a party.)
Levels up to 30th level.
Abilities are set up as “at will, per encounter, per day.”
More elaborate skill-checks and such (based on Alternity rules) for non-combat encounters. (if a party encounters an irate duke, some people could pull up blackmail material with History, the party “face” can attempt to negotiate with him, the fighters can posture and scare the retinue, and overall the number of successes the party gets affects the overall encounter…) I LOVE this, one powerful social character can’t dominate a social situation, there’s still a place for other people’s interactions. In addition, non-combat encounters don’t rely on the NPC’s stats so much, so this rule set can be used for, say, a social encounter with a group of Mind Flayers, so easier to have non-combat situations with antagonistic monsters.
A lot of physical skills were condensed and deleted, but the full range of social skills is still there. Nice.
Climbing, jumping, swimming, just a general strength-based athletics skill, with acrobatics and tumbling a general dex-based athletics skill. Perception, stealth are similarly combined. Ideally, you don’t have to emphasize skills you’ll never use.
Magic items shouldn’t overshadow abilities given by class, as a design philosophy. “A smaller piece of the pie” than class abilities are. Magic item creation is easier, I think they’re abandoning the wacky feats, the massive amounts of time it takes to create. XP costs for item creation is being thrown out, yay! Magic items are in the PHB now, not the DMG—“they’re part of the character’s arsenal.”
DMG emphasizing “why do we do this,” “what tools do you have to craft an adventure,” more than in the past. More advice/guidance.
Drifting away from the “encounter uses up a quarter of party resources” idea in designing encounters/difficulty levels.
In 3.5, monsters were created in a balanced way, like PCs are—in 4th ed, it’s more to create a monster experience, so they’re not creating them in the same sort of power balance as player characters.
Orcus (who in 3.5 ranks very high on the “sexiest demon prince” scale) is now king of hell. Asmodeus is a god now. Demons and devils are really the same thing. The Abyss is now a realm of the chaotic elemental plane. Devils are fallen angels (that’s interesting…) and devils are becoming more human (sad, really, I was really fond of the obrylith.) No more blood war, sad, sad.
Elementals will have emotions and personality.
Dragons: cutting down a lot of the subtypes, particularly in good dragons (they were kind of the same, overall…) Color does not equal alignment, but is more general behavior patterns. Fiery breath will also set things on fire, instead of just doing damage. Overall the game is a bit more dragon-o-centric. Age categories are simpler (fewer categories).
Rules for monster-race PCs in the monster manual, but not very detailed?
General assumption that there’s the same number of monsters as PCs in an encounter, though there’s probably a lot of flex room there (more low-level monsters for a higher-level encounter, etc). Some monsters are more elite (counts as X2 for encounters…)
Zombies! More like movie zombies, less like shambling corpses…braaaains…critical hits may apply to undead, at least with zombies.
Monsters change their behavior and strength as they lose hitpoints (a “bloodied” pit fiend is different, though I couldn’t say how yet, from a “healthy” pit fiend.) That’s really a D&D first. Usually, a hit point is a hit point is a hit point.
Monsters don't have feats! YES!!!
Tactics, combat rolls included in monster descriptions.
“Points of Light”: design assumption. Adventurers are rare. Civilization is rare. Adventurers are powerful enough to leave the safety of civilization to risk searching for treasure in the great frontier, and there aren’t big armies to fight them…
Magic--a lot of non-combat spells (like "Mage Hand," or similer) are "rituals" now, which don't affect your spells per day. So, you don't have to sacrifice combat power for "tool kit" stuff, or vice versa.