Get both - they can't be that expensive can they? DS let me down badly because I spent a year and a half playing Total Annihilation - a game by the same lead guy and still the best RTS produced IMHO. DS virtually plays itself. Typical gameplay is you amass a gang of characters. and a donkey. Assign strategies and set off. Now just click somewhere on the map and your guys will deploy and eliminate the opposition with ruthless machine efficiency, healers healing as assigned. At some point this tactic wil lead to you dying en mass. Now you have 2 choices - either play a game of cat and mouse with the enemy, drawing them out in smaller numbers to be killed by your Terminator-esque crew or slide the difficulty down a notch so you can complete the game as quickly as possible and not feel you've wasted your money. I refer to option b as "My Choice" (I re-read this and had to add something - don't get me wrong I could have finished this game on any difficulty setting, the difference is the amount of pain I would have had to gone through to do this.)(okay, I re-read that last comment and what to make something clear - I am not a wuss for not wanting to gut through the pain. I pierced my own nipple 3 times before I liked the look of it so don't talk to me about pain.)(plus I wore a catsuit in the 70s. Pain? You have no idea...). OTOH with a network of even 2 or 3 computers, or just a few guys or gals you trust over the internet and the game actually is fun. Player roles become important. I had a lot of fun with multiplayer LAN but wouldn't touch general internet online play again.
DD now... no multiplayer but a fantastic blend of Diablo 2 meets Baldurs Gate. I honestly think these games need to decide if they're going to be gutsy realtime games like Diablo 2 or thoughtful almost pseudo turnbased like BG (everything was on a timer but you could pause it). Both DD and DS share the "hit <space> to pause" problem. It does kinda cheapen the game. I'm almost 40 and I still have the reflexes for DII so who are they aiming at? Other than that slight gameplay niggle DD was an absolute joy. Funny, surprising and deeply satisfying. Like a good book. It's on the list to replay sometime just to try out different player levelling strategies.
(And do we have any figures for how much each game sold by? Depressing reading I'm sure.)