Read the last paragraph for a semi TL;DR. The post is wordy for context on the subject.

I originally quit during mid-Cataclysm(Cata) and I remember questing was fairly mundane, primarily pre-Cata. When LFD was added, despite an exp nerf for dungeons, queueing for dungeons as a tank, healer, or with one has been the quickest way to level since. The ability to quickly clear dungeons and have a bonus for accomplishing the random dungeon queue makes it too optimal when compared to other methods of leveling. Since I came back, I decided to level an Undead and I have to say the 1-20 leveling experience is very well done - I had max characters/classes so I had no reason to make a new character prior. How dungeon queueing contrasts to questing or other methods is there is hardly any progression through dungeoning. On my tank character I was able to get from 1-25 in 4 hours - with full boa gear - just running dungeons starting at lv15. On my other character it took me nearly 6 hours to get to 25 - again in boa gear - but I enjoyed the experience much more. Though this experience is subjective in enjoyment, it cannot be denied that a player is doing more with their character when questing.

While leveling, you experience a story, which I believe the Cataclysm 1-60 content did a much better job at wrapping it all together than Vanilla did, but you can gather for a profession, and possibly pvp if your server allows it. When you queue for a dungeon, you might be able to do 1-4 quests, rarely find gathering nodes, and of course no pvp. All dungeons are good for are clearing quickly for the exp and the bonus reward. The early enjoyment in WoW has be dulled because a system for convenience is optimal for leveling, yet hardly enjoyable.

When questing was optimal it was complained against since it was very slow and dull, but I believe with the current Cata content of leveling, players from 1-60 would enjoy the leveling experience much more and understand the WoW universe - dungeoning makes the WoW universe absent if there is no prelude, aka quests. But the immersion is not the only thing that is lacking for the progression of the player, things like BoA gear and dungeon finishing rewards have also deluded progression in the earlier levels.

I leveled my first character, from the time I came back, with no BoA gear and I feel the leveling experience was very quick - /played says 4 days of playing time from 1-90 (I afk a lot). I did a mix of dungeons and quests while leveling this character, but when leveling my others with BoA gear, the experience is noticeably different. When leveling through dungeons, it wasn't until lv30 that I had to repair any of my gear. I found myself still in a division of lv10 gear and my BoA gear at lv30, which is unheard of prior to LFD. When I leveled through quests, I consistently had updated gear and felt I accomplished something when I replaced gear. In my BoA set I rarely replaced any gear. The gear I would replace on my BoA characters often came from the LFD accomplishment and would keep that piece for around 20 levels. As any can tell, the optimal leveling experience involves grinding out instanced areas where you rarely replace gear and you do not experience much of the WoW universe. It boggles the mind when people say that leveling is not enjoyable. You cannot blame people for doing what is optimal, even if it is not enjoyable. Much of WoW is based at max level, but there is much more to be experience from the 1-60 areas and even the other past expansion content.

To improve the leveling experience, I believe dungeon accomplish reward (item and exp) should only be given the first time you finish X dungeon, but the gold reward should remain. In WoD, gear will change based on your spec so the variety of gear will not matter, only the armor type will. This will inherently hurt the dungeon queues during the lower levels, but it will still make running a dungeon at least once viable. I also believe that BoA gear should be changed to a BoA item slot enchant for the exp buff and transmog. For instance, if you give your shoulders a +10% exp, any shoulder armor piece in that slot would immediately have that enchant and would look like the current BoA equivalent. The enchant could be taken off from the character's item slot without being destroyed and the enchant transmog could also be transmogged over if you do not like the look. These two suggestions would give the feel of progression, though the leveling experience would be longer, would also be more enjoyable.