Polymorph spells ARE powerful, but then again I am perfectly fine as a GM with my player gaining powerful abilities instead of hording them all for myself. Disguise Self as an Illusion is pretty limited, since anyone with a good save has a good chance of piercing through the veil of the spell. Relying on Disguise Self is like asking an Efreet for a Wish, as a player you know your character is totally at the whim of the GM while it is much more difficult to imagine a situation where an NPC would notice a Polymorph spell in effect.
Of course, you could reply, there is the Disguise skill to craft a more reliable disguise, but in the world of D&D there are too many obstacles to make them useful. Many monsters are gifted with the scent ability or absurd perception modifiers, meaning it is difficult to succeed on the opposing check you need to pass to actually fool someone by mundane means.
And then there is the whole issue with sex, gender and race. You need to keep in mind that the campaign settings have always featured races with vastly different appearences. No mundane disguise is going to let your gnomish trickster pass for the elven princess` handmaiden, even if he has crazy high Charisma, is fluent in elven, well-versed in royal etiquette, aqquainted with said woman he is trying to impersonate and has advantage on the check because he bribed a laundry boy into "lending" him said handmaidens dress, perfume and accessories.
Now, I`ll have to admit this was a relatively extreme example, but you get a hint at how many obstacles there can be and how many limits there are to the use of mundane disguises.
And guess what: Most problems cannot even be solved by casting Polymorph to take on the appearance of the handmaiden from the example above in the first place! All the spell does for my character here is let him pass for an elven woman. Our poor gnomish friend is still going to blow his cover if he cannot speak Elven, has no idea of royal elven courtesy or fails to recognize members of the royal family.
Long story short, to me, the Polymorph spells were always a matter of trickster`s resolve to create perfect disguises and prey on gullible folks not to turn my caster into a hulking abomination to make the party`s fighter turn green with envy.
If they were to get that feeling riight for D&D Next I`m confident GMs won`t have to complain about Polymorph spells being overpowered. Think about it for a second: Checking out Enworld, catching up with the latest threads concerning the latest edition of D&D and no GM complaining about how Polymorph ruined his sanity. Sweet Elysium, here I come^^
