The definition out of rules of the sneak attack is
Beginning at 1st level, you know how to strike subtly and exploit a foe's distraction.
But following the rules, you can only use sneak attack if you have advantage on the attack or if another enemy of the target is within 5 feet and you don't have disadvantage on the attack.
Does this mean that if the Rogue catches an enemy surprised at the beginning of the first round, he cannot use the sneak attack unless he has advantage?
Since a Rogue with the Assassin Archetype at 3rd level will score all critical hits against a surprised target, and with the new rules the critical hits "If the attack involves other damage dice, such as from the rogue's Sneak Attack feature, you roll those dice twice as well."...