Yeah, I remember PS and PO.
PS was an absurdly good utility spell. You could literally change forms every round, and you weren't limited to animals. You only got locomotive abilities, but this was broadly defined (EGG uses the example of turning into a black pudding to squeeze under a door). In this respect, the 5e version is significantly nerfed.
IMO, the way EGG tried to balance PO, in particular, was pretty bad. Sure, it was something that you didn't generally want to cast on an ally due to the System Shock check to avoid instant death. It could permanently turn them into basically anything, however, so note how EGG had to include a sentence into the spell description saying that creatures prefer their own forms and don't want to be polymorphed. My guess is because some evil wizard player tried to polymorph their henchmen into an army of dragons. I guess that "restriction" doesn't apply to a wizard who casts PS on himself? A spell description that tries to tell me what a character wants or doesn't want is... questionable at best.
Moreover, while the system shock vs death and the check to maintain your mind made it definitely risky to use against allies, it made it significantly stronger than it otherwise would have been against enemies. Not only did the BBEG have to make a save or suck, it came with the risk of death and losing their ability to think like an intelligent creature!
I think that 5e Polymorph is one of the less-well balanced spells in the edition, but IMO it's still leagues ahead of 1e PS and PO in terms of quality of design.