Once you download the installer, the game is yours forever. You do not need to be connected to the internet, nor do you need to deal with launchers like Steam or Epic.
One of the biggest pain points for classic PC games is getting them to run on modern hardware. GOG has done much of the legwork for you. The GOG version of Gothic 2 Gold is pre-patched to run smoothly on modern systems, including Windows 10 and 11. According to user feedback and official notes, it works "right out of the box" with native support for 1080p resolutions and uncapped frame rates, freeing the game from its original technical limitations.