If you get a reroll for any reason you only reroll one die. So if the attack you just made was with advantage and you get a reroll you only reroll one die, not both.
Advantage or disadvantage provides a +5/-5 modifier on a passive check. So a passive Perception (Wis) check used to hear a Stealthy enemy get +5 if the enemy is at disadvantage or -5 if they have advantage.
The Search skill was renamed Investigate (Int). Perform (Cha) was added as a new skill.
When standing from prone it costs you half your movement. This sucks if you’ve got a high speed, but it’s better than taking your full move action.
The double move mechanic formerly known as Hustle was renamed Dash.
You suffer disadvantage when making a ranged attack (with weapon or spell) against a creature within 5 feet / adjacent to you.
You only get one bonus action per round. Making an attack with a second weapon in your off hand is now a bonus action. The Swift casting time was renamed bonus action. The Rogue’s cunning action is now a bonus action.
Now Rogues with two weapons can either attack with the second weapon or use Cunning Action to move again.
When you score a crit you roll all damage dice twice, including any bonus dice like a Rogue’s sneak dice, and then you add your appropriate modifiers like Str bonus.
You don’t track negative hit points. When you hit 0 you fall unconscious. However, if you ever take damage equal to your maximum hit points while you’re at 0 you die instantly. It’s dangerous at low levels, but not likely as dangers at high levels.
You must have 1 hit point at the start of a long rest to get the benefits of resting.
Spells that have the duration Concentration require the caster to make a Concentration (Con) save if they take damage. The DC is 10 or half the damage, whichever is higher. The spellcaster makes a new save after every hit.
But, I didn't think I went anywhere. I've been keeping up the 
