Doom, Counter-Strike, Half-Life, Fallout, Elder Scrolls, Deus Ex
MMod makes such a profound impact on the feel of Half-Life 2 but does not deviate or corrupt the base game where not needed. The combat feels even more fluid and tense than vanilla, with weapons painstakingly remodeled and reanimated for high fidelity and realism. Small gameplay tweaks and visual upgrades such as stunning new particle and lighting effects augment what I would say was already a wonderfully aged game. MMod is a project that keeps me coming back for news of v2, hopefully to come in the not-really-that-distant future. It's HL2 at its best, period.