Cataclysm was the worst expansion by far.
- The Story in Cataclysm was a total disaster, and seemed to be built around a dragon torching random zones.
- Valor Points was a boring and mindless grinding loop. Same goes for grinding all the other currencies, you just do the same mindless and repetitive grinding over and over again, theres almost no sense of having accomplished anything.
- Questing was awful in some of the areas. Some of the quests were bugged and would sometimes show a wrong quest mark on the minimap, plus they gave you little experience and poor quest rewards. Some of the questing areas were awful to navigate through, with hyjal being the absolute worst.
- Gearing up was a pain in the ass in the beginning, with overtuned raids and even if you could do the dungeons perfectly, you were 100% dependent on the other 4 LFD players who were total failures more often than not. It felt like you were wasting your time gearing up for raids.
- LFR in cataclysm is a joke. I realize its supposed to be for beginners, but seriously. LFR was nothing more than everyone rolling Need and then selling the loot to those who actually wanted it.
- Time Gating has never been more obvious than in that expansion. It felt like it was designed to make you waste as much time as possible, instead of giving you an expansion that is enjoyable to play.
- Molten Front is some of the most boring and uninspiring content ever produced in world of warcraft. You would constantly run into dead ends, the rewards are unexciting and mobs are swarming all over you.
- Legendaries were a bad joke. Who got them was based on favoritism and the receiver had nothing to do to earn them other than be the leader's favorite, its disgraceful how blizzard designed this system. What's the point of playing the game if the best items are given to you based on popularity?
- Daily Quests were the same boring and repetitive quests you had to do while leveling up, and they often give you worse gear than you already have. Sometimes it takes longer to get to the actual quests than it takes to complete them.
- Mythic+ didn't even exist, proving the massive lack of content in Cataclysm.
- Class Design in cataclysm is pretty bad. Some of the classes have been so extremely underpowered, and most specializations felt boring and uninspiring to play.
- PvP was probably the worst of any expansion.