Vanilla - 8/10 - New and exciting, raids felt scary and special.
TBC - 9/10 - Not equally new and exciting but content wise, simply amazing.
Wotlk - 3/10 - Raiding started to be dumbed down.
Cata - What comes before 0 again? / 10. - LFR / LFD / flying in EK/kalimdor /
MoP - 6 A turn for the better, devs seemingly care for the game. However, I feel like existing things need to be removed rather than new things added.
As for Serenias post, expansions are not timeless you know. Of course vanilla and TBC raids look easy now because: 1. They were nerfed. 2. The playerbase knew less and were worse players in those days. As for gear dependency, I actually think it was a good thing that you had to prepare to the max to start raiding (both with gear and attunements). Being able to jump in to raids with no gear and a pack of clowns is hardly exciting. This is why I rated wotlk so low and downwards from then. I joined my friends in raiding at the start of wotlk, we were 5 people who knew eachother and 20 strangers. All with no huge commitment, we got server top 10 on Draenor in t7 (which is, or at least was pretty competitive in pve).
Also, in wotlk and cata, the community was I feel dragged down by LFD/LFR/crossrealm and in MoP just to add fuel to the fire we add Crz. I think they should have done server mergings somewhere where the amount of players in the game started going down (and they still haven't, are you kidding me?). People ask: well, would you want to play wow without LFR/LFD/BG queue every where (as well as tons of other new things that make the game more and more convenient. Yes, of course I would play that wow, that's the game I fell in love with in 2005.