This is not to say that I haven't tried achievement hunting before. I did it just to see what the game could offer, and, honestly, people aren't missing much.
Let's take the loremaster achievement as an example. If someone decides to do it, they will be driven in the warcraft universe, and introduced to the lifestyle and events there, but the problem is that most quests from the classic zones (Kalimdor and the Eastern Kingdoms) don't actually tell you anything exciting. They just follow a dull formula: "Help! X is terrorising my farm/village/land and it needs to be stopped. Kill Y amount of X/bring me Z from killing X.", or "X stole my Z. I want it back.", or "X has something valuable, which I want to possess. I want you to kill X, and bring me the item(s) to me.", or "X is terrorising this land. In order to undo the damage, you need to kill X, grab their object, go to the area and cast this spell". I'm prolly forgetting other formulas, but you get the idea. They are repetitive.
TBC and VVrath quests are way better - they actually give you bits of information about the main villains - and thus the time spent doing them is imho rewarding.
Admittedly, not all achievements are boring or pointless. The "world events" category is enjoyable, since players get to celebrate the ingame festivals, as if they were there. So, that's good design. The exploration achievements are also nice, since they incite the players to explore the zones and see how its inhabitants look like. As a bonus reward, the player unlocks various flying paths, and if at one point they decide to go back to the old areas and farm achievements/veins/herbs, they will reach them faster.