The game comes with many new features and improvements in regards to the original version, which you can access simply via the launcher that comes included. You can adjust the resolution, the type of graphics, the window color, in addition to many other options.
Also, a really awesome feature that Zelda Classic comes with is a map and campaign editor, which allows you to create your own Zelda levels, and even change the graphics.
Putting these details aside, Zelda Classic is exactly what you would expect it to be: the original game, with the original story line and gameplay, but designed so you can play it on your keyboard by just double clicking the shortcut on your desktop.
Zelda Classic is currently one of the greatest ways to play the original game from the saga. It is truly indispensable for videogame enthusiasts, and will make the nostalgic fall in love, and allow those who didn't experience it in their youth discover completely new worlds.