According to Gearbox president, Randy Pitchford's,
latest tweet, the fifth playable class is now available - a week ahead of schedule!
Gaige the Mechromancer is Pandora's newest Vault Hunter. Decked out with powerful skills and the accompaniment of a giant robot partner named Deathtrap, this half-human half-robot chick can kick some serious ass. She reminds me of a steampunk Mordecai.
Those who preordered get her for free as part of the Premier Club while those who didn't can still buy the add-on for a sweet $9.99/800 MSP on PSN and Xbox Live, respectively.
Let us how Gaige plays and if she's as good as they say. See you in-game, hunters!
Update: I have bought the Premier Club DLC and created a Mechromancer; my opinion of her is very positive. I can very well say she is quite a lot of fun to play as, despite being a girl. Deathtrap comes in very handy, as well, when being swarmed with bandits and especially Badasses. Too bad it has a time limit before it has to recharge.
I highly recommend you try out this class. You will be pleasantly surprised.