Doom 1/2 is pretty easy to run.
-Get the DOS version from a freeware site or buy one of the games on steam
-Get ZDoom and ZDLauncher
-Go to settings and add Doom 1/2 .WAD under IWAD and ZDoom under Sourceport
-Then download one of these mods:
-Brutal Doom
-Russian Overkill
-Trailblazer
-Guncaster
(The last 3 are bassicly Gun Mods wich have some pretty over the top but amazing weaponry)
(I also advice Ketchup.pk3 wich is availible on the Doomworld Forums for Russian Overkill,Trailblazer and Guncaster since it amps up the gore a bit)
Basiclly after this just drag and drop one of these mods into the WAD section in the Main tab of the launcher and your good to go!
(Russian Overkill,Trailblazer and Guncaster are best served with Ketchup.pk3 wich you then just drag into the WAD sction too.)
Hopefully this is a good explanation on how to play doom mods.
Edit:Russian Overkills Weaponry might lag slightly but not to crazy.