Well… Cata was an extremely ambitious project. Basically all 1-60 leveling zones questing were fully re-done in addition to the usual zone content for the new levels. So there was a hell of a lot new stuff, and compared to what came before, questing was easier, more accessible, and with less travelling times than ever. For someone who wanted to see the lay of the land by leveling new characters, it could even be overwhelming. That said… quantity isn’t quality, and it is very easy to see which zones and stories got the time and focus they needed, and which ones were just made barely functional and filled up with meme-quests to get done. And there is a lot of that around. While WoW took itself quite seriously before, now you’ll find obvious parodies and joke quests that don’t even pretend to really fit into the world all around.
So… a bit of a mixed bag there.
On the factions… well, in the leveling zones most Horde questing is about defeating the Alliance in one way or another, and (since the Horde had way less zones than the Alliance before and the devs decided to create parity on that) they take quite a lot of zones too. Not to mention that Alliance cities suffer way more from the enviromental changes than Horde cities. So… Southshore is destroyed, Menethil Flooded, the Nigh Elf harbor destroyed and replaced, the Loch drained, and so on, before the story even starts, while the Horde expands rather than retreats. Not a very happy time to play Alliance, frankly. I didn’t play much Horde, either, but I get the impression that Horde players were happier with the leveling changes the more they were into the faction war. The Horde really is on a War Path under a new War Chief.
Oh yes, they made Thrall abdicate to focus on his shamanism and killed Cairne in a novel between expansions, so that a warmonger now leads the Horde. If you want context, you might want to read The Shattering, or a summary of it, because the game won’t really explain much.
Now, that’s the 1-60 stuff, the 80-85 stuff is way less about the faction conflict, and thus way less one-sided against the Alliance. And big names like Thrall don’t play much of a role in that, yet. All the zones have an element of helping allies like druids and shamans in fighting back the Twilight Cultists and their elemental allies that seek to bring the End Times. They are mostly fine, though half of Uldum is basically just a way too long parody of Raiders of the Lost Arc… Horde and Alliance are only seperated in the Twilight Highlands and those are a banger for either faction, with great dwarven fun for the Alliance, and dragon riding hardocre orcs for the Horde.
The rest of the addon story isn’t too bad, either, frankly. Stop Ragnaros once again with the help of all the important druids, with a bit of drama in between, get a weapon to combat Deathwing by time travelling around, and face him together with the dragon aspects. It’s fine. It does make Thrall the clear protaginost though, chosen to save the world, and the player feels like a bit of a tag-along, which was once again especially jarring for some Alliance players who didn’t really appreciate the “Thrall abdicated, so you like him now”-thing. To be honest, he isn’t even around that much, but well… he is treated like Green Jesus, Chosen Saviour of All, or so the memes went. I didn’t find it that bad, and honestly, WoW has done a lot worse since with main characters. But well, the change from player-focussed story-telling to npc-character-focussed stories was pretty apparent there.
I guess that sums up most of it.