I've been playing MoP since its release.
I enjoyed the leveling and the new experience because I was getting quite bored of Cataclysm. The pet battles are fun for a while but do get quite bland and I also was not found of the Monk class.
Playing a Pandaren is fun as again, it's a new experience and doesn't make things seem boring.
However, getting to endgame content, I was rather displeased. Blizzard offers a LFR feature (Looking For Raid) where you can queue with randoms from across the realms to run through dumbed down 25 man raids. This has been around since Cataclysm but I just feel it takes away from the difficulty.
In terms of PVP, it broken. All characters come with a base resilience of 65% and if you gem full resilience, you're lucky to hit 70% resilience. Players now PVP in endgame PVE gear and killing a healer is close to impossible.
After playing for 7 years, I'm still in favour of WOTLK.