Twilight Highlands is especially egregious. The Alliance story in TH is disjointed, and incoherent at times. After the wacky ride with Fargo, you wake up in the unfinished Alliance base (which never actually gets finished) under attack by the Horde. After fighting the Horde off, you go to the shore where you are attacked by the Horde again. After defending yourself, you then proceed to spend the rest of your time in TH planning a Dwarf wedding, trying to save your alcohol from the Horde, and eventually making it to the Red Dragonflight, who are really angry at you for some reason.
The whole zone is spent pushing to Bastion of Twilight and Grim Batol in an offensive against the Twilight's Hammer. The Horde attacks are barely acknowledged. The closest Alliance players come to replying to the constant attacks is when they steal a bolt of cloth from a goblin zeppelin, which is used in the Dwarf wedding. There's also the puzzling problem with the Red Dragonflight being so pissed off at me. What did I ever do to them, besides assist them against the Mad Aspect of Magic in Northrend, and rescue Calen from that dank pit in Silithus?
The problem lies in unfinished content. This video has datamined sound files from the Cataclysm Beta client. The first half are lines from Thrall that eventually made it into the Goblin starting zone. The second half are lines from Varian in what was supposed to be the Alliance's Twilight Highland's intro.
Varian was supposed to uncover Benedictus as a traitor in a quest line that echoed of the old Great Masquerade quest. A high ranking traitor using their influence to spread dissatisfaction among the people of Stormwind? That links together most of the internal problems that were faced in the Human starting zones, in particular in Westfall. Furthermore, note the direct instructions to not engage the Horde. That fleshes out Varian as a character, and most importantly, it ties the entirety of the Alliance questing experience in TH together. You're not lashing out at the Horde because your King commanded you to focus on higher priorities. That little scene was the keystone for pretty much the entire human questing experience in Cataclysm, and Blizzard dropped it for a cheap reference to the lead quest designer. Way to go.
This still leaves the unusual welcome you get from the Red Dragonflight. I'm a hero to Alexstrasza, Exalted with the Wyrmrest Accord, and I get treated like I've been associating with someone who kills baby red dragons for fun and profit like the Dragonmaw Clan. The quest makes complete sense for the Horde players, who just spent the whole zone rampaging with a group of orcs best known for imprisoning the Dragonqueen against her will and using her children as weapons of war, to be used until broken, and then discarded. Blizzard just never got around to making an Alliance version, and the Alliance story suffers because of it.
Just as painful was the treatment of the Worgen experience. Everyone remembers the plans for the Worgen District in Stormwind, it was planned to be in the park. It made sense, because after the Gilneas set, then the Worgen players could quest in Duskwood, WPL, EPL, and the Blasted Lands, you know, the parts of the game that have Worgen involved quest lines? Instead, Blizzard deleted the park, and sent them off to Darnassus where they sit in a tree and get handed green and grey quests in Darkshore, where the quest givers call them Night Elves. That was how rushed the transition was for Worgen players. They didn't even code the race into the drop box for some of the quests in the zone they exiled that race to.
What I find most frustrating is that they had the tech to make it a compelling story. Hell, they had the story to make it a compelling story. Instead of blithely shipping the Worgen off to Kalimdor, what they should have done was make the Worgen's next questing zone another phase of Gilneas. Instead of the Night Elves showing up, have the 7th Legion show up. Leveling through Silverpine, one of the most chilling moments was during the phased incursion into Gilneas, when you find a field strewn with shattered Elite Abominations and the dismembered corpses of Deathguards, with one survivor left, who recounts the story of the men who came and destroyed them without mercy, and left him alive just to spread fear among the ranks. Through the magic of phasing, the worgen players could have been there, fighting the ugly war, the guerrilla war. Give them phased incursions into Silverpine, just as the Horde players got into Gilneas. While the Horde players rez Godfrey, Walden, and Ashbury and tear through the Alliance forces, the Alliance players should be stalking them with Crowely and Ivar, seeing the damage they wrought, and seeing the story out to its conclusion, the forced withdrawl of the GLF to Stormwind. It would have been great, it would have set the tone for the Alliance quests in Shadowfang Keep, and it would have put the Worgen in a position to experience what little questing they had outside of Gilneas. Just a couple more phases, and a few more quests. That's all that was needed. But they ran out of time.
These mistakes break down the fabric of the story. They break immersion, and make things much less interesting for the players who have to deal with these jarring, fractured, and frayed transitions. Perhaps more damaging than the damage to the story is the damage that things like this do to Blizzard's reputation. Cataclysm took a lot of luster off Blizzard's good name. There was a running joke when it came to Blizzard, Soon™. Much like Valve's "When it's done!", Soon™ meant that Blizzard wouldn't do this. They wouldn't rush an unfinished project out the door to make it in time for the Christmas rush. When players asked a question and got Soon™ for an answer, they knew that they were in for a wait, but they knew that the wait would be worth it (Except for Starcraft:Ghost, but what's a little vaporware between friends?). With Cataclysm, Blizzard has lost the trademark to Soon, and with it, they've lost the trust of the player base.