" When asking someone about a place or person...I've learned the structure:
What's ____________ like?
What's Rio de Janeiro like? "

Yeah, you got/learnt it right. Most textbooks have this grammar point.
For instance: the "Essential Grammar in Use", here´s the link
at
 http://books.google.com/books?id=2RznagcL9o4C&pg=PA98&lpg=PA98&dq=%22what+is+it+like%22+grammar+structure&source=bl&ots=pppdHmacBj&sig=lP7fMsUp_hpoRLmWRFkrzNRqSKE&hl=en&ei=LvuUTfyhOoPI0QGHnpX6Cw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CCcQ6AEwAw#v=onepage&q&f=false
On Page 98.

Hence, "What´s Rio de Janeiro like?"    -  okay
                What is it like Rio de Janeiro?   - wrong, or not standard way, that is it caught your eye!

But,  in a dialogue:
          "I lived in Rio de Janeiro for fifteen years?
          "Really? What is IT like?
=======================================
    Why is that? because you knew beforehand that I lived in Rio de Janeiro, so IT replaces RIO DE JANEIRO.

BUT, again, no "what is   IT    Rio de Janeiro like?"
(big no no,  because  it would be as if you were somewhat saying "What is RIO DE JANEIRO (IT) RIO DE JANEIRO LIKE?.

Stick to one of the two following forms =>
1) What is Rio de Janeiro like?
2)  Or if  IT (Rio )  was just quoted by somebody "What is IT like?"
-------------------------------------

     Now, as Fran pointed out, it might have been a informal and conversational context,  so it could be implied "how is it to living in downtown" or "how is downtown like'' (the description of the landscape etc...)

     May be acceptable form in certain situations, in English you have to adapt the culture of the speaker (not always that literate or academical), but it is not very usual (even not natural, most of times).

      So, Fran hit the nail in the head (hehe) on that one, as always she learns how things work in real life pretty fast.

     When I grow up I want to be like this!

     Thanks.

      Hope it helps.

     PP.