Heh, that's your intimidating backlog? Mine has...let's say a bit more than those. If 20-ish intimidates you, I don't want to think what mine would do to you. Pray you don't reach that point.
Anyway, leave DMC3 for later, I say, you'd probably want to replay it on a different difficulty and with Vergil (although he's just replaying Dante's levels with his own playstyle) so it would take longer. Unless you just want the story, in which case a run through on Easy is quite fast.
Disciples 2 (excellent choice, by the way) is slow. I'd suggest you turn off attack animations after you get sick of them - units do this fancy twirling and chanting and sweeping and stuff that takes several seconds. For each attack they make. Each unit. Several times per combat. It's interesting to see but it extends some battles by several times (the easy ones). Even then, it's not that fast - four campaigns, each with several maps, even if you don't completely restart or reload too much, it still takes a while. And then there is the expansions - the Light/Dark ones add in roughly 50-60% more campaign time, I've yet to play the one with the elves (I suppose you have it, though).
MDK I haven't played but I've played MDK 2 - if that's anything to go by, move it towards the top of the list - it's quite fun and relaxing game, not terribly long but quite enjoyable.
Rock of Ages I sort of assumed isn't really long, so probably toward the top of the list is fine for it.
Thief and Witcher I think you can put roughly towards the middle.
