You'd be joining the game at what I would say is quite a bad time. There are a lot of things wrong with WoW and its community, mainly caused by features and mechanics implemented in later expansions by Blizzard which have both discouraged the social aspect of the game and encouraged poor and often frankly terrible behaviour in players. Most people playing it have been playing for a long time and many are suffering burn-out.
The latest expansion was meant to 'fix' a lot of things that some people - mainly a vocal minority on forums - thought were wrong with Wrath of the Lich King. Despite a revamp of much of the gameworld - which is mostly empty now - Cataclysm has failed to reinvigorate player activity, which is less now than it was a year ago.
There is still a lot of fun to be had in WoW, but for many the magic has gone. Read http://eu.battle.net/wow/en/forum/topic/1951296771 and http://us.battle.net/wow/en/forum/topic/2369922419 to get some idea of current issues.