I was thinking of picking up The Lords of Midnight and Doomdark's Revenge since they're on sale, but I'd like to know if there's any replay value? I know there are three different ways you can complete the game, but are there random elements or is everything pretty much fixed?

Doomdark's Revenge is endlessly replayable, since it's much more dynamic (due to CPU controled lords moving on their own) than Lord of Midnight. And you can set your own goals, like trying to recruit all lords, trying to recruit only Good lords, only Fey etc, etc. Lords can also be killed in duels against other lords, addding to the dynamics of the game. Also, all the items (128, I think) are all randomly distributed each game.

LoM is more predictable since the lords don't move (but it's also a tighter war game than DR), and they can't be killed while still having soldiers under their command, but it's still quite replyable if you try different strategies, like how "high" you want to defend against Doomdark's hordes, and which direction to send your starting characters.

Thanks!

I decided I'd give both games a shot!

Good decision, I can assure you!

As said, Doomdark's is always re-playable.

And you can try several ways in Midnight. About this let me give you a bit of advice:
try first to know where your future Lords are and Waters of Life for regain full vigor and Cups of Dreams to
renew the day. Then you can choose informed strategies.

Have fun.