That really depends on what type of game you like. If you like computer role-playing games, there are some great old titles that are still a lot of fun, even though the graphics may be a bit dated.
One of my favorite series of old CRPGs is the "Gold Box" series of Dungeons and Dragons games published by SSI back in the late 1980s and early 1990s. These were not the first D&D games, but they were the first to really capture the experience of playing the game. The first title published was "Pool of Radiance in 1988, and this was followed by three sequels: "Curse of the Azure Bonds," "Secret of the Silver Blades," and "Pools of Darkness."
SSI published other D&D games, including two games set in the Savage Frontier and a trilogy set in the world of Dragonlance. They also published a construction set called "Forgotten Realms Unlimited Adventures" that let people create their own titles. There is still an active community that uses UA to make adventures, and hundreds of modules have been uploaded over the years.
The Gold Box games are available for purchase from GOG.com, and have been updated to run on modern systems.