Spectacular stand-alone buildings like the above are great for making your name as an architect, but in European cities, already chockablock with architectural gems, I like the fitting-in style of design which has the fancy name of "Contextualism". If ever a single building defined this approach, it's this one:-
It's modern, but it works as a perfect compliment to what's there already. Together, each building looks better than they would've done on their own. Instead of slap-in-the-face architecture, this is well-mannered architecture that respects, even enhances, the past.