The whole polymorph chain is broken
I don't think the 3E designers have worked out a 'reasonable' polymorph chain yet. In fact, if I run a game in the near future none of the polymorph chain will be available, and I would strongly consider the variant wildshape abilities from UA rather than allowing wildshape (with or without Natural Spell...) An Ogre, for example, has a LA of +2 to help represent its strength, constitution, reach (and other advantages of size) and natural armour; in addition the Ogre takes 4 levels of monstrous humanoid (a definitely sub-optimal class....) A Wizard, with a single 4th level spell, can effectively give the target at least 2-3 levels worth of increased power!
At least part of the problem IMHO is the plethora of creatures in the sourcebooks (both Core and non-Core,) and the great disparity of their abilities, strength-to-HD ratio, humanlike-enough-to-cast-spells-vs-not-humanlike-enough-to-cast-spells, etc. It also breaks the general pattern of spells, in that rather than enhancing natural ability scores, it provides for fixed physical ability scores (the only other spell which did this in 3.0E, divine power, was changed to an enhancement bonus for 3.5E)
I might favour a spell which transforms the caster into a certain fixed form, with the level of the spell depending on the bonuses thus granted. This would allow a fairer comparison with other spells. For example the ogreform spell might give enhancement bonuses of +8 Str, -2 Dex, +4 Con, +4 Natural Armour and Large size - making it in effect a combination of Enlarge Person, Bull's Strength, Bear's Endurance and Barkskin, with an additional Str bonus and Dex penalty to balance it.
Now what level would you put a spell that acts as a first level and three second level spells all in one (actually, the 'real' polymorph is much better, because the changes to ability scores that it grants aren't classed as enhancement bonuses, so stack with further spells or magic items....)? Is 4th level fair? Now consider that polymorph gives freedom to choose from a huge number of forms (many of which will be more effective than the Ogre form, or give access to flight or other special movement methods in addition to physical power)
Anyway, sorry for the appearance of being off-topic - but my point (in a roundabout way) is that if polymorph is irrevocably broken, then shapechange is hardly even worth considering.