played vanilla wow from beta till tbc came without getting bored once, never a dull moment.
played tbc untill wotk came out, same again never bored always something i needed/wanted to do that i actuly enjoyed doing.
Wotk i ding level 80 finish naxx in next to no time quit the game about a week later no specific reason just got bored i couldnt tell you why exactly just wasnt doing it for me.
Cata dinged 85 finish my 5 man heroic get bored before even raiding same again cant give a reason as to why.
MOP dinged 90 very enjoyable leveling if im honest, get my heroic gear in about a week done some raid finder and now im bored again no interest to even start raiding properly again no idea as to why.
point beeing the last 3 expansions havent kept my attention for the long haul like vanilla and tbc did, now this just could be down to the fact iv played the game for so long all the excitment and novelty of raiding has wore off or that they are just bad expansions. either way I will continue to keep buying every expansion that comes out because i really want one to get my full attention again but untill that happens im happy playing vanilla on a private server, still my personal fav.