LFD was introduced about a year after WotLK was released if I remember correctly. Back then I and many others instantly said that this is a mistake. Just like the cross-server battlegrounds have been a mistake. But this one was on a much larger scale: The PvE scale of WoW.
Well, players are often wrong. But this time we have been right. There would have been nothing wrong about supplementing WoW with some kind of cross-server PvE content. But that's not what Blizzard did. Instead they replaced major amounts of PvE content, all group-content except for raids, over-night. My comment over at Azuriel's place is this:
You may be right that WoW never put you into groups, but the way I came in contact with the server communities in classic and TBC were instances and battlegrounds. I met the same people (who played at similar times like I did) again and again. Eventually we would start talking; putting each other on friends lists to be able to invite each other when we wanted to do a instance – or even farm elites in the open world.
We started to know each other. Eventually people would tell me that they finally want to make their own raid and if I wanted to join – just a test run tomorrow evening?
This is how it worked. This is not how it works anymore.
I am not drawn into any community right now with my priest. I would have to make a very proactive decision to join a guild and then spend weeks to get to know those people. That's not how it worked in the past. I remember when I was the main tank of my raid in TBC that when doing an instance I was constantly on the lookout for good (and friendly!) players who might join my raid. In the beginning I, too, was asked to join raids, later people knew whom I already tanked for. Major parts of the server community knew each other. This added incredibly much to WoW !
There would have been nothing wrong with adding a few extra cross-server dungeons to WoW (e.g. during leveling), but to remove all the content that made the community know and depend on each other was a fatal mistake.
But it wasn't the only one. The second big mistake was the trivial leveling game. And I am not talking about making it faster. I wouldn't have a problem with a faster leveling game as long as I didn't dramatically outlevel my opponents. But even not-outleveled opponents are terribly trivial until level 60. And never become dangerous again.
Moreover, there is no variety. All mobs of the same level have the same number of HP, which you can even see displayed. Some have some special moves, which are irrelevant, because they won't even scratch your health points.
During level 4-9 in the Undead starting area there is some resemblance of danger for completely new characters. This makes this starting zone incredibly fun. You really feel immersed and not like a detached tourist.
Finally the third big mistake of World of Warcraft is the endgame character power progression. I wrote an entire series of posts about that before. The quintessence is that the mechanic that has been introduced with WotLK makes you gain itemlevels relatively fast until you hit a ceiling and then that's it for a few months. You can come back a few months later and do it again. This mechanic makes the absurdity of the system very, very apparent. Why would a designer want to do that?
Classic WoW provided reasonably challenging content that players could experience in a pleasant social environment at their own pace. And this applied to all players; from the most hardcore to the most casual. WotLK and Cataclysm herded players together at one difficulty level by requiring them to regularly experience trivial monotonous content in an unpleasant social environment. Classic WoW was far from perfect. But the character power progression mechanic was superior to the one we have now, for everybody but the top 10% of raiders.
You also know my opinion on why they did this: Because WoW is mostly run by hardcore raiders who just want to do scripted raids for their own sake. That's all they want from WoW. But it is probably the part of WoW I want the least. Furthermore, the hardcore raiders are part of estabilished communities. That's why the LFD doesn't affect them much and they don't need to care about how well WoW pulls people into communities.
Last but not least there are several smaller mistakes.
The core combat has become too fast, in my opinion. It's often stressful and not suited for players of age 30+. This is especially true for PvP, but also for PvE. Combat is too much about speed right now and, consequently, not enough about pressing the right buttons and moving to the best positions, unless you mastered the speed first. Most importantly, this speed just doesn't feel right to me.
The power progression at all times in WoW is too fast. This causes all kinds of problems. It would have been easy to fix this with Cataclysm, but apparently Blizzard decided against it. They should understand that gaining new abilities and thus exploring and mastering your character is what makes leveling fun. Gradually doing more damage which isn't even a direct consequence of any specific action of yours, adds only very little to the leveling game.
Heirlooms and low-level PvP are ridiculous for new players and anybody who likes to engage in it without grinding for heirlooms first.
There's no incentive at all, not even an advantage, of leveling in a group of even two players, let alone more. I'm not an advocat of forced grouping, but that doesn't mean that grouping should be discouraged or even be outright ridiculous.
Mobs are often too large. If my sword can only hit the opponent's feet, sometimes only the toes, that's a problem in my opinion. If I can't even see my whole opponent, but only his legs, that's also a problem! The alternative, to zoom the camera out a lot, leads to not seeing your character anymore. That's not good; period.
Spell effects are often absurd for a melee. The screen is full of magic explosions, while you would like to see the effects of your sword hitting the opponent.
Character advancement gained in PvP is not usable in PvE and vice versa. I know why this was done in TBC, but I still think the advantages don't outweigh the disadvantages at all. Raiding just to gain equip for raiding and PvPing just to gain equip for PvPing not only rips my character in two halves, but also reduces my incentives to do either of the two.
Starting without any PvP equip at all at max level is absurd. Expensive crafted items whose existence a new player can't possibly guess don't help much.
Much of the late-game five player content is badly tuned for melees. Ranged classes are almost always superior, because they take less damage.
The leveling game 1-80 is neglected. Ironically after Cataclysm hit. Things like being unable to defeat even two opponents at level 4-6 in the undead starting area, but killing scores of them at level 20 and even more at level 30 is one proof of this. Learning curves for all kinds of activities are messed up! Professions are useless unless at max level, especially non-gatherer professions.
The TBC, WotLK and Cata transitions during leveling are far from perfect. And I am not even talking about the story. More polish is needed!