Well the only way to become "fallen" is to begin your game as a regular paladin and get your rep below 6 (i think). The drawbacks are that you lose all your paladin special abilities and you gain....nothing. (except for some custom weapons i designed

)
I found that the class was not only more challenging, but also more interseting because of the way people react to you. The element of roleplaying the "rouge" always appealed strongly to me but its not for everyone. (actually i used to shadowkeeper to change my alingment to chaotic evil, just to add to the feeling)
If you want to play as a paladin, then they are a excellent class, because of their semi-wepon specialisation and their various resistances, abilities and immunities. You'll want to specialise in 2 handed sword, for the AVENGER!!!
Mainly I found because of their immunities that paladins were way better at taking punishment from the undead and dragons\deamons and the 50% magic resistance goes a looooong way to defeating mages!
And dont forget EVERYONE LOVES YOU!!!!
hope that helps!
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