A while back Bethesda took the Unity ports of Doom and Doom 2 made for consoles and added them to the Bethesda launcher, making the 90s shooters run at 60fps with widescreen support and an add-ons menu via which you could download things like John Romero's Sigil in-game. As of today, the Steam versions of both games have also been updated.
When you hit Play you'll have the option to launch the DOS versions, and your WADs should still be fine. I just fired up GZDoom and played through the first level of Doom 2 with my preferred settings and it's still the best way to experience it, but I'm glad the default versions new players are more likely to see are getting these improvements.
Here are some of the changes.
- A crosshair that changes color when targeting an enemy, which can be turned off in the menu.
- Ultra-Violence+ difficulty on the level select screen, with fast enemies like Nightmare and deathmatch/co-op only weapons spawning in.
- The logic error that prevented the message "Picked up a medikit that you REALLY need!" from being displayed if you grab one while below 25 health has been fixed.
- The bug that made Doomguy's "ouch face" only appear in very specific circumstances, rather than whenever you take 20 points of damage or more, has also been fixed.
- Split-screen deathmatch is based on "deathmatch 3.0", which means weapons remain after being picked up, while ammo and items respawn after 30 seconds, excepting invulnerability and invisibility.
- The end-of-level timer includes milliseconds for all your speedrun needs.
You can read the full patch notes at Slayers Club.