So, wait.
We get the expansion but not the actual main game?
Or is this both?
...confused...

'Features: Expanded Gameplay: 4 campaigns and 15 stand-alone scenarios, plus the original campaign and 13 scenarios from Warlords III Reign of Heroes.'

So best of both world really.

Warlords III DLR is the STAND ALONE SEQUEL TO 1997’s Turn-Based Strategy Game of the Year and includes all features and campaigns of the original Warlords III. In addition, Darklords Rising has too many enhancements to the AI, game options, diplomacy and multiplayer to list here. Page 9 -13 of the manual details all the amazing extras that this game has to offer to make your head spin.

Right, got it.
Thanks!

Where is the original campaign?

EDIT:
I remember it as having FMV cutscenes. Did I just dream those?

Reign of Heroes had FMV cutscenes. And a proper intro. My CD version of Darklords Rising does not have them, which is very unfortunate. I really like Lord Bane taunting all the time...

Also, as far as I can tell, music is different between the two versions.

This is a shame! I remember really liking the theme that those FMV's brought the game. I wonder if there is some way of reimplementing them, or if GOG have any plans to release the PROPER Warlords III.