First check out this trailer:
Skulldash is a mod based on Doom 2 and the advanced GZDoom engine that turns Doom into a speed-running, score-chasing arcade game. Each of its 40+ levels is littered with Skulltokens. Grab enough of them and the way to the exit opens, but be quick, you’re on a timer. It’s got new weapons, enemy variants and bosses, and a hub with tier-based level progression. And of course it’s free. The original Skulldash was released a couple years ago, but the Expanded Edition released today adds far more maps, the score system, and a ton of polish.
Want to try it out? You’ll need the mod itself, the latest version of GZDoom, and a copy of doom2.wad. (You can buy Doom 2 from Steam or GOG, or pull the old floppies out of your closet if they still work.) Unpack GZDoom and Skulldash to a folder, copy doom2.wad to that same folder, drag SkulldashExpandedEdition.pk3 onto gzdoom.exe, and you’re ready to play.