essentially Wrath blew stat scaling way out of proportion, deathknights were horrifically implemented, PvP was more or less ruined by tiny health pools compared to the enormous burst added by the stat scaling issue and damage coefficient scaling itself. PvE got kind of toned down to reach a wider audience and balance issues really went untouched to a degree that put the issues in BC to shame. Vehicles were poorly implemented, wintergrasp was for the most part a huge failure and fell short of the isle of quel'danas in a big way. Not even going to talk about Ring of Valor and Dalaran sewers. Mana pools essentially became infinite due to the same stat problems so instances like Ulduar had to be balanced more around huge burst damage on tanks to force the healers to spam nuke heals, since mana fights were gone. This was clearly reflected in the stat priority for tanks which was stamina before all else. You may have noticed every tank stacked as much stamina as they possibly could, this was due to huge spike damage from bosses that would sometimes outright kill a tank foolishly based around avoidance (which was previously important to save healers mana, pure health tanks like feral druids were called "mana sponges" for a reason. Luckily there was no problem just beaconing two tanks and spamming holy light all day) There were more but essentially it was a travesty compared to BC. The one thing I will admit Wrath really did well was that it did a pretty good job of making most specs of most classes viable in everything. In BC oomkins were all but useless, there was usually only 1 viable raid dps spec per class, In arena you usually only had one largely viable spec and the rest needed very niche builds around them (ie if you said "druid/warlock/rogue") everyone knew the druid was resto and there was a really good chance the warlock was sl/sl and the rogue was whatever the latest fotm build was) elemental shamans only existed in 5s, 2v2 and 3v3 was only resto shamans or enhance in certain meatcleave comps which were even then pretty rare. However, since they didnt try to make every spec viable in every possible aspect of the game it made the game way more balanced as a whole. They didn't have to worry about frost's dps in pve when balancing their pvp burst because frost was for the most part a pvp build and arcane or fire was mainly a pve build and that was that. So essentially a large portion of WoW fans (at least the ones I knew, which were all relatively dedicated WoW players) were heavily disenfranchised by wrath and almost all devout wow players admit it was a downgrade quality wise.