German (and other Western-style) knives tend to be heavier and made of “tougher” but “softer” steel. They are also generally made from thicker blade stock, which means it takes a bit more pressure to slice through foods. What’s more, these knives are typically sharpened to a wider cutting angle (20-25° on each side of the blade), again requiring more muscle to cut through foods. Because of the “softer” steel, German steel knives will also get dull faster and require more maintenance. Many cooks find that they need to hone their knives before each use.
Japanese steel knives are generally lighter in weight and are made of thinner, harder steel. Due to their harder steel, the blade stock can be thinner and the edge more acute—that is, sharper—than a comparable German knife. Shun knives, for example, are sharpened to a 16° angle on each side of the blade. The lighter, thinner blade makes Japanese steel knives like Shun extremely agile, precise, and can even be less tiring to use.
This is not to say that German steel knives are “bad.” (In fact, the softer steel enables them to take a bit more edge abuse.) It’s just that Japanese steel knives are different creatures. You may find that you need to refine your knife technique in order to take full advantage of the light precision that Japanese steel knives have to offer. For instance, if you’re used to simply pressing downward to make a cut with a German type knife, with a Japanese knife you want to make sure you slice by moving the knife forward or backward. This avoids crushing the food, enables the thin, light blade to glide through whatever you’re cutting, and helps you make a very precise cut.