Things to Expect:
-Building your own settlement seems largely inspired by Wasteland Defense. If you do a youtube search for this mod, you'll undoubtedly find AlChestBreach playing it, if you're curious.
-Damage Resistance appears to be the defensive stat
-Project Nevada seems like an inspiration for power armor, both in the HUD it provides and in how each piece is customizable like Project Nevada's implants.
-Crafting appears to be largely inspired by New Vegas, though crafting systems for tools such as weapon repair kits and wasteland tequilas (recipes) may or may not be a thing, with the crafting we saw focused more on housing and weapon mods
-The Rock-it Launcher made an appearance, suggesting the specific weapon schematics of FO3 will likely return.
-You can call in a vertibird. wut.
-Bobbleheads were shown, however their purpose or effect is likely altered (see below)
-A deathclaw seems to do a "killcam" on the player at one point. This could imply Skyrim's killcam system will exist in FO4, at least to a degree. This is hopefully tweaked from Skyrim's version to be less frequent or not activate on players so readily
-Voiced protagonist
-U GET UH DAWG
-Pip-boy minigames
-A bit of speculation, but expect about as much weapon variety as FO3. Todd said "over 50 base weapons," FO3 indeed has about this if you only count weapon types (aka unique sniper rifles or unique 10mm pistols not counting as types) Further variety is provided by the weapon mods.
-A new defense type represented by a lightning bolt. Perhaps bullet and energy resistance are seperate...?
-Critical hits no longer seem random, but "charged." You can command a critical hit to take place, then doing so again requires that the meter recharges.
-"Hold Breath" appeared while aiming with a scope in the footage, suggesting the game might exhibit more first-person shooter elements.
-Sprinting is listed as a thing. Endurance lets you sprint further.
-A big airship exploding during the footage had the Brotherhood of Steel emblem on it along with the name "Prydwen." It's safe to say the East Coast Brotherhood is here.
Things to not expect (whether confirmed missing or unlikely):
-Skills are missing
-Weapon degradation and armor degradation seem gone; the pipboy display shows nothing for these, meaning repair as a skill may not even be represented by perks and is completely gone even in "spirit"
-Damage threshold
-No signs of a hardcoe mode seen
-It is difficult to imagine skill books being a thing with skills gone and all...
-It's also difficult to imagine many speech/skill checks going on with the new dialog menu; only four options exist at a time, so including these would either neccesitate excess menu scrolling in dialog ("hit X to see more options") or neccesitate that only three options are provided and the fourth is unlocked based on character SPECIAL. I honestly don't see them doing this.
-A bit hard to imagine them bothering to record "idiot dialog" for low intelligence characters.
-Driving was a feature speculated upon which has yet to be shown.
-Traits