People like to go to the birthplace or former home of famous people because they feel a connection to the people, and because they can better understand the context of the person's life. Also, England is fascinating and a fantastic vacation spot.
I am not sure why this is such a huge tourist attraction myself. While, as others have said, you can see his birthplace and grave, I would prefer to visit the Globe theatre myself.
If you happen to be visiting that area and are a huge Shakespeare fan, then it is worth the trip to see the birthplace and finally resting place of this genius.
One reason to go to Stratford would be to see Shakespeare plays performed. When I visited, I got to see Captain Picard ;) play Antony in "Antony and Cleopatra". You can also see the birthplace of William Shakespeare, and his grave. It is touristy, but worth going to if you are in the area.
Well, the main reason that people would go to Stratford Upon Avon, England is because it was the birthplace of William Shakespeare. There are many tours and museums there that are solely devoted to Shakespeare, his life and career. There are also historic castles that people enjoy visiting, and I even believe that there is a little theme park for younger children.
As the birthplace of Shakespeare, Stratford-Upon-Avon holds many historical interests and sights. The town is mostly devoted to his life and work, but it also includes many great period-style structures (like the castles previously mentioned).
The main reason why people visit the town, however, remains the ongoing intrigue surrounding Shakespeare, his life, his times, and his body of works. Those who love the language love the town, and those who are enamored with the work of Shakespeare, in particular, visit frequently to feel more "in touch" with him.
To be honest, your question is a good one. Stratford upon Avon is a tourist trap. It lives on its Shakespeare connection but doesn't really have anything to show for it. It isn't very historic and there are no genuine Shakspeare-related sights except for the cottage that his wife, Anne Hathaway lived in. If you are asking this question because you are considering a visit, I would say you shouldn't bother. There is a theatre (The Royal Shakespeare Company runs it) but that is about the only real Shakespeare connection. Also, in the summer, it is FULL of tourists and the tourist industry.
Shakespeare lived in Elizabethan time. Stratford is not an Elizabethan town anymore. It is a modern satellite town for the large city of Birmingham nearby. I don't know which 'great period structures' other posters are alluding to. And there are no castles. There is an old church, but it's not a particularly fine one. Shakespeare lived his working life in London, not Stratford. We English feel a little sad that millions of tourists are sent by their travel agents to Stratford. They usually combine it with a trip to Warwick Castle (in Warwick not Stratford) which is another tourist money-fleecing excercise.
If you want fabulous well-preserved old English cities/towns I suggest Oxford, Cambridge, Bath, Winchester, York, Ludlow, Chester and, of course, London. There are many others, but not Stratford.
I'm in Manchester. I couldn't recommend it to tourists!