Like Airget said i don't feel the current beserk makes a lot of sense.

However looking at traditional aspects of the effect, most of the time when you are berserk you have increased attack at the loss of defense. and in a lot of older FF games you lose the use of abilities.

Essentially i feel that berserk should increase AA, but not really abilities. similar to spinning heal for pug. perhaps an increase in crit rate for autoattacks, say by 50%. and put it on a timer rather than wearing off when you are hit. (or maybe terminate when you are below 50% hp)

But i don't think a lot of people will like that, because right now the majority of damage comes from WS, not AA. so maybe just a straight increase of attack and lower max HP by a %.