Sadly the GOG version does not have Duke Nukem 1 and 2. The only place were you can buy them these days seem to be the 3DRealms website.
But with the GOG version you can play Duke Nukem 3D in eduke32 which supports high resolution texture packs, real colored lighting and higher screen resolutions. Just requires a little bit of setup and a good enough PC.
Post edited August 31, 2011 by Gabelvampir