Interesting city - biased opinion
My opinion is biased. Shanghai was my first stop on my first trip to Asia, so you have to keep in mind the culture shock and differences between where I come from, where I've been, and China. Shanghai is an interesting place. Exploring some of the local neighbourhoods was the best part for me. Getting to see local restaurants and stores, understanding the differences between the areas, and hunting for culture. The famous skyline and tourist destinations felt a little forced and contrived.
Insider Tip:Get the people at your hostel to write in a paper for you, in chinese, whatever you might need (I am vegetarian and this SAVED me). Once you do that, getting lost, on and off train stations is the best way to see the city. Don't bother with the Maglev, its a waste of money and nothing special.