LOADED QUESTION. lol
I rate it an obvious 10.
I have played it for four years. Starting with a smushy healy type.
ALOT has changed and improved since then.
One thing being that they have lowered the level requirements for mounts.
Yes, some quests require a bit of going back and forth, but one reason for that is because you get several quests at one area and that will also be where you turn them in when you are finished. Spot A to pick up quest, B to complete it, then back to A to turn it in. Sometimes they will have another for you sometimes you move on. As for the traveling, a reason for that is so that on your way you can kill mobs to loot items for resale or simply skill off of the xp.
The developers spend ALOT of time and careful detail on the world, so there is a lot to see. You get special achievements now for exploring all of the lands. It's also one of the things that sets WoW ahead of a lot of other MMOs.
A good rule of thumb is to remember it is for fun, so if you do pick up a quest that frustrates you, simply abandon it and get a different one. ;)
There is a FANTASTIC addon for questing now that makes it a lot quicker. It's called Quest Helper and you can download it safely from Curse.com. Anyone in WoW will tell you that it is a must have. It helps you find hard-to-find mobs/items and puts all your 'needs' on your map so you can gather everything as you go in one swoop.
I would go to Curse.com for all the WoW addons because it is the safest. You can also search there for addons that are offered for your specific class you are playing. So no, you don't need ALL the WoW addons, just what is useful to you as you progress.
Along with the one I already mentioned, there is also one called Gatherer that remembers where you gather your profession items and marks them on your minimap so you can find them easily there after.
The rest are pretty class/level specific depending on what you are looking for.
It all comes down to personal choice so I'll give you my opinion. But there really isn't a 'right' answer here because the choice is yours. :)
If you like Warhammer and the Diablo games, you'll love WoW.
Blizz has pulled a lot of things from Diablo and used it throughout the game.
Aside from the usual content, WoW has in-game events and celebrations based on Holidays.
It also has a new Achievement system that rewards you for some of the achievements, such as special pets and titles.
While the current level cap is 80, next year is the new Cataclysm Xpac and the level cap will be 85.
Other than questing, there are Dungeons and Raids you can do with friends/guild (or strangers).
There are PvP areas (battlegrounds) and there are large cities to RP if that is your thing.
There's a reason it's one of the world's largest MMORPGs.
Hope this helps you decide. Good luck and happy gaming!