I've beated the first 2 campaigns over 3 times already
I've completed prophecies with my warrior, elementalist, and monk and beaten factions with those same characters plus a ritualist (who I deleted later since ritualists are boring to play). I also have a ranger that needs to do the last two missions of factions and is almost done with the crystal desert part of prophecies.
BTW, in case anyone hasn't played in a long time, Anet had released a few weeks a new game mode called "Hard Mode" which allows players to replay the campaigns at a harder setting once they completed the campaign and are level 20. The AI in this mode is ridiculously harder (they attack 33% faster, cast 50% faster, run 25% faster, and recharge their skills 50% faster) and are levels 22-30. They also have some really nasty elite skills equipped and will kite and run out AoE attacks much sooner than in normal. The incentive to do hard mode is that it nets you way more experience and gold and the quality of the items dropped are much higher (they nerfed the drop rate in normal mode so you have to do hard mode to get better items).
The cake is a lie... THE CAKE IS A LIE!!!!!