Doom 2 is the commercial version of doom 1, and seeing how they don't want to rip off the people who bought the original doom, they made more levels and more enemies, and the one new weapon.
Uh... really?
That's odd. Doom 2 was a new game with some additions. And improvements to the game's code.
But more levels? Uh, no, they were all brand new levels.
More levels implies it's an add-on to the original doom.
Like the 4th episode was in The Ultimate Doom.
Are you sure the shareware was sold in stores? Because I'm mostly certain it's illegal to sell things that are free to download. Without proper Permission. Plus, making people pay for something that's not the full version is kind of mean.
And Doom's shareware was free to download, because it was uploaded by the people who made Doom, to an FTP!