What game mods have you played and loved? Purists won't like it, but sometimes mods make games even better than original!
For WA the greatest mod was ProjectX of course. For Blood the best mod/addon is Death Wish, it's totally cooler than original I think. There's also a pretty interesting Median XL mod for Diablo 2 and it allows playing online even if you havent bought the original game

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For WA i'd say Wormkit/Rubberworm, Project X requires too much faffing around so I never got into it, perhaps if it was easier to install and run, there's a chance i'd change my mind, but Wormkit and Rubberworm give me everything i've ever wanted, bar real time worms.

Arma 2- DayZ.

DayZ - Unlimited Stamina.

Quake 3 Arena - Urban Terror.

Cities: Skylines - Traffic Mod.

Fallout 4 - More building. (There's a limit on how many things you can build, this mod takes away that limit.)

Rocket League - Bakkes Mod. (Rocket League sucks now because Epic, as usual, ruin everything.)

Struggling to think of other games i've played with Mods.

Btw HoMM III: HotA, very large community, a lot of enhancements, additions, new cities etc etc