Guard Break
Despite the outright deletion of defensive options like ground recovery, typical mixups in Street Fighter EX are weak. Few characters have overheads, cornered opponents can't be crossed up, and crouch teching is very potent.
Without meter, blocking is overly strong. There's very little the player on offense can do against turtles aside from humble frametraps and tick throws. With meter, SFEX becomes a horror game.
For one bar, every character in Street Fighter EX gains access to an advancing, unblockable attack. On any hit, Guard Break stuns the opponent and lets you land a max damage followup. Guard Breaks can anti air for juggles and often auto shimmy or outright beat bad pokes in the neutral game. In EX1 specifically, Guard Breaks don't use your meter until their first active frame.
Kara Guard Break
Because Guard Break is interpreted by Street Fighter EX as a special move, you can kara into it with any grounded normal to enhance its range.