1. her voice is music to my ears.
the metaphor is the sound of her voice to pleasnt music.
2. life is a roller coaster with all its ups and downs.
the metaphor compares life to all it ups and downs.
3. the world is a stage, and we are all actors.
the metaphor is comparing the world to a theatrical stage.
4. love is like a rose with all its thorns.
the metaphor compares the experience of live to a beautiful but difficult flower.