It's no secret that gamers love the Half-Life franchise, even if Valve doesn't seem too interested in it anymore. That love means that even without a Half-Life 3, or Half-Life 2: Episode 3, gamers are left making their own games and ports to satisfy their Freeman urges. In one instance, that leads to games like Black Mesa, which port the original Half-Life to the newer Source engine and in others, like Half-Life 2: Classic, it means taking the more modern game in the other direction entirely.
Half-Life 2: Classic is a reimagining of the popular sequel as if it was made back in the late '90s. That means redoing the lighting, the models and enemies, retooling the maps and levels to be much more barebones and completely removing the physics model that so defined many of Half-Life 2's puzzles and character interactions.
The mod is available to download from ModDB now and offers quite a sizeable chunk of Half-Life 2 demade gameplay in it. It's not the entire game, but it's the first time a mod has offered so much of the experience in this state. As PCGamesN points out, others have attempted to backdate Half-Life 2 before, but no one has taken it to quite the same level.
The developers have now expanded their team to 10, but face a difficult decision. How retro do they make the game look? Some think the art style should retain the Half-Life 2 style, while others think models and setting should look more like the original Half-Life. Let them know on the mod-page what you think.