Shanghai is the first city where I've come out of the metro (from the airport) and been instantly "wow'd". The buildings are tall, everything's lit-up, and the city has a very modern and hip feel to it. There's lots to do and see around Shanghai - from modern shopping districts, the site of the First Congress of the CPC to the house of Sun Yat-Sen, you'll never be short of things to do. Will definitely come back!
Insider Tip:Walking through Shanghai at night and enjoying the sights was great, but being constantly approached by women and young guys asking if I "want a massage" or "want a lady" became extremely annoying, so be on your guard but don't let them get under your skin (a simple "no" will usually get rid of them). Also be careful when crossing roads as, like other places in China, a green pedestrian light doesn't necessarily mean it's safe to cross.