Stopped raiding in ICC so i dont have any experience from cataclysm/mop. The game was slow back in vanilla, everything took a very long time to do. I was up in felwoodgrinding essence of water for over 12 hours and i ended up earning 150g after i sold them on ah. My point being that for the people who got to see naxxramas and kill Kel alot of hard work and alot of dedication was required. I didnt mind not getting to see all of naxxramas, i got to see the kills thru movies.
When wow became a oversized cash cow and all the subs was at it's peak i think they decided that people who bought wow which is a pve game should be able to see all the pve content, cos thats why they bought the game right?
I was a raider in vanilla,tbc and wotlk and i think i had the most fun in ulduar. Hardmodes and killing the boss in a new and much harder way was very exciting to me.