Having played the game from what is known as 'vanilla', but also spending time to try out other mmo's as they came, i can say that i have an un-bias view of WoW. Also be advised that most original 'vanilla' players have already left WoW, most the player base is from the 'WoTLK' time, which was the easyiest expansion of the series, that is why many people find Cataclysm 'hard'.
Make no mistake,WoW 'was' a great game back in the day, but it has not aged well graphicaly, and nor has it aged well in terms of difficulty.
WoW is a victim of its own success, Blizzard's constant updates continualy make the game easyer so that it can attract a wider audiance. It also seems that Blizzard is ether running out of expansion idea's, or is loosing their imagination. As shown in their latest expansion "Mists of Pandaria".
Nowerdays it is much easyer to talk about the good points of WoW than the bad, since there are so many bad points. So...
The Community: The community is huge, you will always be able to find groups, chat, and generaly have fun.
The Compatability: The game is old and so it can easyily be played on old computers even with the latest "improvments", of which i use the term loosly.
The size: The game is big, very big. Plenty of exploring to do, tons of gear, and alot of lore.
End game access: its very easy to get into endgame content, no-one can really be left out.
Ease of use: The games controls are very simple, point, click, press.
Now for the bad points, as i said there are to many to list, but ill go over some atleast.
All the good points above are also partialy bad.
The community being huge will ofc mean u will innevitably bump into the "less civilized" types of people known to prowl the internet, unfortunatly for WoW, its large population of younger players also means simularly immature confruntations are frequent.
The compatibility is there becouse the game is outdated, and thus doesn't look anywhere near as good as pritty much any other mmo out there atm.
The size of the game when actualy playing seems small due to leveling speed, you will miss alot as you level, and the fact that less than half the content in terms of gear is actualy usable, old engame content is almost never used.
The ease of use also makes the game boring to play, the point click press style gameplay gets tiresome, there is no challenge.
PVP: Now this area is heavily argued with plenty of 'anti pvp' and 'pro pvp' communities out there, however in a non bias opinion, PVP in any game that uses 'Gear',Random Number Generation,'Specs',or anythign else that is not determind by a players PVP'ing skill, is not proper PVP. Therefor i will advise that if you want a game for PVP look for games that have set layouts for your character,ship,car, etc so that players are competing on a level playingfield. In WoW the winner of 'most' pvp battles is decided by gear and class/spec. very rarely is skill involved, which is why WoW and pritty much all other mmorpg's are not concidered eSports.
For me, the main issue is simply the difficulty of the game, not only in terms of content, but also in terms of how the game plays. Its far to easy now, unlike in its 'vanilla' days, this inclues 'Cataclysm', as although slightly harder than 'WotLK', it is still far easyer than 'vanilla' and 'TBC'.
It will ofcourse be around for a while longer due to its immense player base but if your looking for a mmorpg to play, do your best to look else where first, WoW is not a great example of a good MMO.(Its a great example of good buisness though).
Please note that i am nether 'pro' nor 'anti' WoW. This is simply a un-bias review :)