ScoreDoom makes playing & re-playing Doom wads more fun in both single-player and multi-player co-op, without changing the standard Doom game-play and feel. ScoreDoom is built from the modern sourceports GZDoom & Skulltag, so it has modern OpenGL graphics and client-server architecture. It adds an arcade style scoring system to Doom. Points are primarily scored when shooting/killing monsters, achieving map objectives, finding secrets & map items in the quickest time possible. Points are also scored in many other fun ways, like chaining kills together in a short time, causing extreme (gibbage) deaths, heck, even blowing up barrels gives points etc. There are high score tables you can set locally, or take on other players across the world on the global online high score leader-boards! Else take on other players around the world directly in competitive online co-op mode! ScoreDoom also has an Add-on Pack that adds up to 300 new Doom-like enemies, many new power-ups and other cool stuff.
This is actually not a modification, but a source port. It's based on ZDoom, GZDoom and SkullTag (the predecessor of Zandronum) for multiplayer. It complements perfectly Doom's arcade gameplay by adding a scoring system. This is a feature that should exist in the default game, and I give it a 10/10 rating because of this.