Personally I feel the polymorph spell as it was was too powerful, much too powerful in fact for a low-magic item setting.
Troll form has 5 regeneration, whilst zombie form has 10 resistance to bludgeoning, slashing and piercing. Back in the days of being level 11, my wizard could go to Demonologists, round up all Aberrations and Fanatics and just stand there with Ethereal Visage, Zombie Form and Acid Sheath whilst the monsters promptly killed themselves at me. It was free and very fast XP. Same could be repeated at then much more powerful Scrags and for loads of other monsters.
And troll form with it's 5 regeneration was a quick way to heal up free without having to bother with heal skill or going to an inn. Not all useless in combat either.
At the level you get Ethereal Visage, pretty much no monster ever hits you for over 30 damage, and even when you only have Polymorph Self, you can still get good XP by picking monsters that mostly hit under 10.
Personally I feel that 10 damage resistance for turns/level against all physical attacks is too much for something a level 7 wizard gets, even that it stops her from casting other spells.
EDIT: Thinking of it, it'd be nice if forms like Troll and Zombie weren't now useless for all but RP purposes. Perhaps +1 or +2 regeneration for Troll and say, 3 damage reduction for zombie?