These are the lasting things that Half-Life 2 gave us, besides headcrabs and crowbars
Briefly

Valve's Source Engine set a precedent for modular game development, allowing continual improvements and innovative technologies to be integrated over time, an approach uncommon in gaming.
Half-Life 2 not only piled on innovations but also refined existing ideas, making it a cornerstone in the evolution of narrative and gameplay mechanics in video games.
Read at Ars Technica
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