While lighting is important, not using halflife.wad and going above the original budget of 500 polys per "scene" is what makes modern works look much better.

Most of the original textures are under 128×96 px and some suffer from awful palletisation artefacts with purple and orange halos. We still cannot use more than 8 bpp but we can use 512×512 textures and do a better job at reducing to 256 colours. I use pngquant for that.

In GoldSrc lightmaps cannot get more intricate though, they're tied to the texture scale so you cannot get a finer lightmap unless you also make larger textures and scale them down, and these two combined will wreck your "AllocBlock" budget in which all your textures and lightmaps must fit.

ericw-tools and its dirtmapping are still welcome improvements over the "traditional" *HLT compilers.