The biggest change is in its graphical look. Day of Defeat already had some excellent texture work for its levels on the older Half-Life 1 engine but adding detailed textures to Valve's Source engine gives the new port a new lease on life. Indeed its one of the best, if not the best, looking WWII games ever made with some excellent character and weapons models as well as some excellent level design on the four revamped Day of Defeat levels. Physics in the new version is limited to ragdoll death animations for characters and some small items in the levels like barrels so don't expect a lot of objects flying around a la Half-Life 2 Deathmatch. Valve also decided to put in support for its heavily hyped high-dynamic range (HDR) lighting feature (which will be used in a more profound way in the upcoming free Half-Life 2: Lost Coast level). Most gamers are familiar with the "light bloom" effect which makes the lighting in a game look like one is looking through a camera lens. In Day of Defeat, HDR is used more subtly. Light in the game, whether coming through the sun or in a light fixture, is softer and glows more realistically. You may not even notice it until you look at a wall and notice a brightening in light before its glow calms down a few second later. It's a small thing but it certainly makes the level look less artifical.