Actually, Rieslings can be dry. Rieslings are a very difficult grape to cultivate and turn into wine, which is why it is so rarely produced when compared to other grapes such as Chardonnay or Pinot Gris/Grigio. Rieslings, more than any other white grape reflects the "terroir", or environment of which it is grown in. While a grape like Chardonnay can be made into a wine that will taste like whatever you want it to (depending on what's done to the grape during the winemaking process), Rieslings are very finnicky and develop a character all on their own.
In a nutshell, Rieslings from the top three regions in the world tend to take on the following characteristics:
Germany - Sweet to very sweet, and much less dryer than the other regions. Lots of tropical fruit flavors such as pineapple, lychee, passion fruit. In general, the least complex and my least favorite of the major Riesling producing regions.
France (Alsace) - Dryest Rieslings with balanced fruit flavors, which tends to pick up a lot of stone type fruits including peach and apricot, with some citrus like tangerine. Most floral-type aromas of all Rieslings which usually includes lilac, roses, and violets. Alsatian wines also tend to have the most minerality of all Rielsings due to the growing conditions. IMO, the most complex of all Rieslings and one of my favorite white wines.
U.S. (Oregon/Calif. Central Coast) - Well balanced in all aspects in dryness, fruit, etc. Cheaper Rieslings tend to be more on the sweet side and while the pricier ones tend to be more dry.