Duke Nukem Atomic edition is the most rated FPS on gog. Is it worth getting? Does multiplayer/deathmatches online still work?

I think it's totally worth getting. I don't know how well the multiplayer on GOG is though since the game runs on DOS so you'd probably need an IP address or LAN connection. I'm sure you'd be able to find some third-party software to help you find others to play multiplayer with (gameranger, hamachi). I haven't played the multiplayer but I still highly recommend the game if just for the single-player.

okay and there is a HD graphic patch I can install with this version?

yeah, It pretty much turns it into a PS2 era Duke Nukem 3D with actual 3D sprites and weapons and dynamic lighting. You can find it on the Mods forum which can be located either through the community page or from the store page for the game in the "about" section. I took me a couple tries to get it to work but it eventually did and it looks pretty nice!

get meltdown, you get the game plus a few others for free. More people play meltdown than the steam version as well. Heres the link: http://duke3donline.com/Players/index.php