Well the expansions are probably the best reason right now to own it IMO. I have the old CDs for those, but the installers don't work on modern PCs and you have to go through a hassle to get them working. And then you can't have them installed at the same time as the original Duke3D, you have to overwrite the game files... unless you want four different installations of the same game. Which works, but still kinda annoying. Here you just launch the game and it lets you choose what to play instantly, each with their own new hi-def menus btw. Looks really nice.
Later on though they'll be adding multiplayer which will hopefully include coop, I'm really looking forward to that although there probably won't be too many people playing online after the first week or so I'd imagine. But coop through the original and expansions? That'll be awesome, I could never get Caribbean or Winter to work for that. And I also read that one of the upcoming features is more expansion packs... I dunno if that means old crappy stuff like Duke!Zone 2, but if that means new custom-built episodes by Devolver Digital I'd be psyched.