"You're something else"

What does "you're something else" mean.
it sounds silly, but it's hard for me to grasp the meaning. i've always believed that it was a compliment, but I am no longer sure of that.

It usually is a compliment. It expresses admiration without containing much specific meaning. But you have to pay attention to the tone of voice, too. If the speaker is sneering, then it's not a compliment.