Düsseldorf is the capital of North-Rhine Westphalia, and with its population of just under 600,000 people, the city is the second-largest in the state. Just down the road from Cologne, the cities apparently have a strong rivalry - much of which is based around beer.
According to Wikipedia:
People in Cologne prefer Kölsch while people in Düsseldorf prefer Alt. Waiters and patrons will "scorn" and make a "mockery" of people who order Alt beer in Cologne and Kölsch in Düsseldorf. The rivalry has been described as a "love–hate relationship".
Perhaps it's because of the strength of this rivalry that the cities are so strikingly different from one another. Cologne is imposing and really has a feel of history - maybe that's down to the almost Harry Potter style proportions of the cathedral, it really sets the tone for any trip there. Düsseldorf on the other hand may not be so visually striking - but it has a feel of modernity and there's a groovy, laid back feel to the city - which has a lot going on in the media and advertising industries.
Expats abound in Düsseldorf - no doubt down to the fact that not only is it a nice place to live, there's a robust economy and a very definite feeling of condidence in the future. So if you're sitting in one of the city's great coffee places (even the Düsseldorf Starbucks branches feel like independent coffee retailers) then don't be suprised if you hear Kiwis, UK people, Americans and so on. This is a cosmopolitan kinda place. And that's something further underlined by the city's large Japanese population - and there are some authentic Japanese restaurants too -well worth checking out.
Another of the city's many plus points is its proximity to Belgium and the Netherlands, meaning that you can go and check out various other cool cities and be home by teatime.
As expat locations go, this one is pretty special. Of course if you're planning on an extended stay it is important to get all your research done before getting on the plane. Check out this Guardian article for one expat's interesting experiences living in Berlin. She mention sin the article that if you want to work in a bookshop in Germany you need a specific bookselling degree that takes five years. Now, that could explain why so much in Germany just seems to work effortlessly - it must all be in the training!