Change isn't scary, however Blizzard presented the new Execute in a very bad way, No other class(apart from Warriors, but still, it's way easier) has to spend their resources to use an execute ability that alternates the play style a lot for the last %'s.
Monk: No execute¨
Paladin: Hammer of Wrath, no HP cost
Warlock: Doomguard, instant cast with long duration, Drain Soul eases the rotation for Affliction, giving you way more resources
Mage: No execute
Hunter: Kill Shot, no Focus cost
Rogue: For assasination; simply switching from Mutilate spam to Dispatch spam
Priest: Shadow Word: Death, no Shadow orb cost, instead, generates 1.
Shaman: No Execute
Warrior: Execute replaces everything except for Colossus Smash and Bloodthirst(If sufficient rage).
Druid: For Feral, Ferocious Bite refreshes Rip, which is their main Bleed at Execute range.