The Walther P38 was the standard issue German sidearm of World War II, so by that measure, it’s not ‘overlooked.’ But one aspect about the P38 that is heavily overlooked is its influence. For example, the Beretta 92FS, or the standard issue sidearm of the United States military since 1985, is basically a design copy of the Walther P38. Furthermore, many modern day pistols owe their heritage back to the P38. The double action and single action firing system for the P38, combined with the safety and decocking lever present on the side, was groundbreaking for the type and largely came from the Walther PPK pistols from earlier.
The P38 continued to be used as the standard sidearm for the German military and police up until 2004, when it was replaced by the 9mm Heckler & Koch USP, also known as the P8. This certainly says a lot about the overall design qualities of the P38 pistol. Today, the P38 really is one of the most under appreciated pistols ever made.