I've played both, although I haven't been able to force myself to finish DS yet.
DS: If it were any more linear, the thing'd be in a straight line (wait, it is a straight line!). There's little to no thinking involved in playing it - just get your characters to drink potions now and then. The rest... Well, set them to auto attack, and that is that. The characters, NPC or controllable NPCs, have no personality. The story is boring, typical, and cliched in every aspect. It, in my opinion, is worse than Diablo in regard to combat. Pretty graphics, good idea in including beast of burden, but there's nothing else going for it.
Divine Divinity: The combat is very much like Diablo's, but the game offers far more in term of dialogue and story. It is highly enjoyable, although not very different from most other RPGs. At least, you'll be able to familiarize with it pretty fast.