(In addition, AD&D polymorph was pretty weak. I don't recall it giving ability score bonuses. Maybe it gave multiple attacks and base AC, which could presumably go out of control, but it was nowhere near as strong as the 3.x version.)
In OD&D there were two polymorph spells:
Polymorph self and
polymorph others.
Polymorph self allowed the user to take the shape of the desired creature, but does not grant "the combat abilities of the thing he has polymorphed himself to resemble". (The example given is that the caster gets neither the attacks nor breath weapons of the of a dragon, but they would be able to fly.)
Polymorph others, on the other hand, is permanent and "gives all characteristics of the form of the creature." There is also a vague reference to "not necessarily the mentality, however." Both spells require system shock checks.
In 1st Edition,
polymorph self is similarly limited in that it gave you nothing except "the form of any creature and its form of locomotion", but it no longer required a system shock save and also gave the caster the ability to change form multiple times during the duration of the spell.
Polymorph other, on the other hand, was essentially identical to its OD&D incarnation except that the vague "not necessarily the mentality" reference had been turned into a defined system for determining whether or not a targeted creature would assume the personality and mentality of their new form. But, yeah, it gave you
everything from the creature.
2nd Edition closes a loophole in
polymorph self (no noncorporeal forms, dammit) and adds mode of breathing to the list of traits you acquire. (I should probably add breathing to my
polymorph fix, too.)
Polymorph other has gotten massively more complicated in an effort to deal with weird loopholes and special cases (like casting the spell on shapechangers against their will), but the major change is that it's limited the abilities gained to "physical abilities" (which it then attempts to define). The system shock and potential mentality shifts remain.
3.0 eliminates the system shock saves and mentality check for
polymorph other, but tries to replace it with some new balancing methods: The new form can't increase your size by more than one step, can't increase the target's HD (and can't have more than 15 HD), and doesn't get the supernatural or extraordinary abilities of the target. Other than that, it's pretty much identical to AD&D2's
polymorph other.
Polymorph self, on the other hand, has received a massive power-up because it's functionally identical to
polymorph other except the caster can change their form multiple times during the duration of the spell.
3.5 tosses out the old tradition of
polymorph spells almost entirely, but most of the changes actually served to make the spell even more powerful as a combat buff: More drawbacks are removed from the spell (like the Will save to avoid disorientation found in 3.0) and the target is granted the extraordinary abilities of the new form. (Looking at the 3.0 spell next to the 3.5 spell, it's almost impossible to figure out what the 3.5 designers were thinking with this one. The reduction in duration was implemented on buffs across the board; it's unclear why they felt this would justify massively increasing the utility and power of
polymorph.)
