This could be wind or frost damage. The leaves should re-sprout in a few weeks.

Yes, that's exactly what I was going to say. My Acer always looks stunning until a freaky cold windy day some time in May always comes along! I sometimes cut off the damaged leaves - they are usually only the outermost top ones - depending on how ugly it all looks. they will keep producing new ones as Volunteer says, and it will soon look better again. Try to keep it out of windy spots would be my advice.