Does Blizzard allow people to buy and download the first diablo game online? Or do I need to purchase a physical copy?
No, you cannot purchase the original Diablo game, in digital or physical form, from Blizzard's online store. The game still appears to be available on Amazon for either the PC or PlayStation.
If not, you can try searching for other releases or bundle. In 1998 there was a re-release bundle called Diablo + Hellfire. Blizzard also released a Game of the Year Collection in 1998 that contains the original Diablo. The Blizzard Anthology, released in 2000, also contains the original Diablo game. The Diablo Gift Pack contained the first two Diablo games but no expansions. In 2001, a Diablo: Battle Chest was available which contained the original Diablo, Diablo II, and the Lord of Destruction expansion.
Diablo II, however, is still available from Blizzard's online store. The original Diablo II game, Lord of Destruction expansion, and the Diablo II Battle Chest (which includes the Diablo II, its expansion, and strategy guides for each) are all there. However, the Battle Chest for Diablo II does not include the original Diablo game, but Diablo II and its expansion are available for digital download.
The Diablo 2 Battle Chest comes with Diablo 1 game.
Diablo 1 is now treated as abandonware and can be downloaded online from archive.org.
- First, download the game here. You can mount this .iso file (right click --> Mount on Windows 10, slightly harder before), and then install Diablo by launching AUTORUN.EXE from the newly mounted Diablo drive.
- Then, download the 1.09 patch from here to the same folder that you installed Diablo, and launch it in order to update the game. This is the only official patch from Blizzard you'll need.
- Finally, install the third party patch from here as well, which fixes a lot of startup and graphical issues and allows you to play at various resolutions, in windowed mode, and etc.
If you want to play with friends, you can utilize GameRanger or Hamachi to play multiplayer games on simulated local networks nowadays, despite Battle.net discontinuing support for the game early in 2018.