What is the theme of the play, A Midsummer Night's Dream? Is it love? Dreams?

In considering how fantasy versus reality operates as a
theme in A Midsummer Night's Dream, one needs to look at the role
of location as an important signpost in how this theme is made
manifest.

The world of reality is represented by Athens,
where all is law and order and everyone knows (or should know) his or her place.  The
opening scene in which the ruler, Theseus, must render a judgement of law is a great
example of how this real world operates.

On the other hand,
the woods, are a place of fantasy, of magic, and this world is open to topsy-turvy
events that have an air of chaos about them.  Notice the opening scene in the woods. 
Titania and Oberon don't speak with the same accord that Theseus and Hippolyta do. 
Titania doesn't treat Oberon as the ruler he is; she doesn't give in to his rightful
supremacy as the male leader.  This absence of law and order gives much room for the
fantasy and magic that transpires in the woods.

Truly, the
woods are such a magical place that Bottom and Demetrius remark on the wonder and magic
of the events that have transpired there.

There is an
interesting combining of these two worlds at the end of the play when the fairy King and
Queen (and Puck) make an appearance at the Duke's palace after the wedding celebration. 
It suggests that these two worlds of fantasy and reality are maybe a little more
connected that we might have expected.