TFC - Free mod but spend thousand and thousands of hours on publics, clan games, skill maps, puzzle maps, I don't think there will ever be this much versatility in any game ever again. The HL1 engine is just so amazing, you can do almost anything with it. It may not be realistic by todays standards but it's simplicity was what lent itself so well to modding. The way you could move through it the character really felt like an extension of your body, not like todays games with ridiculously low FOVs, head bobbing, all kinds of smoothing, and just general clunkiness - all I get from these is a headache and motion sickness.