"you are really something" usually implies a compliment, similar to "you are very special, you amaze me" . However the meaning could change depending on the context :)

I guess it depends on how you say it. But the first meaning that came to my mind was "You are really an idiot. What a piece of work." But you can also use it when you are especially grateful to a person. As you can see, "something" can be either good or bad.

'you are really something' = you are a person whom I admire deeply

……you are somebody to me.