Not worth, its an old game and you would have to spend lots of money to get all the expansion.... Wait for newer game or look for new game now
All the expansions except the most recent (Mists of Panderia) are included with the basic game now. No need to buy BC, WOTLK, and Cataclysm. I expect they'll roll MoP into the basic game once the next expansion comes out. It's also unnecessary to buy the expansion at the start.
Unless you play everyday, it will take months aswell.
After lvl 70, after lvl 80 and after lvl 85, the exp needed for the next lvl is colossal.
When was the last time you leveled up a character? They've been chopping down the amount of experience needed to level. In 5.3, they cut the experience needed to get from 85 to 90 by a third.