looking at the beta rules for "shapechange" the spell seems woefully underpowered for a 9th lvl Wizard level spell (not sure how it plays out for other classes). I understand that the 3.5 version was powerful and had to be capped. I even accept that the spell chains are a reasonable compromise. But they do not work at all with high level campaigns.
I realise that Pathfinder is focussed on lower/intermediate level play, but as it stands, except for the ability to fly/burrow/swim etc (which you could get with a low level poly variant) there is no good reason to use a higher level spell varaiant when you are a playing a high level wizard.
You're essentially useless in a fighting role:
- your BAB is used, +9 @18th lvl for wiz
- you get a paltry +5 to your BAB for the strength increase *at best*
- if you have average strength that's an amazing +14 attack bonus,
- I'd be surprised if you hit any decent 18th level foe with that (AC34+ seems common) And that's the primary attck - -5 for the next and ...well...
Yes, you could be buffed, but even that won't add more than what, +6 to strength...? so + 3? hm. still, not much help.
Ok, so physical attacks are not useful. Ok, - what about other/supernatural etc? Severely curtailed. Ok, I have bo problem with that. To a point. lets take Form of Dragon 3 (a mighty 8th level spell) - an awesome 12d8 (save for half - or evade for none).... every 1d4 rounds (so what, twice in a combat?) And a few other odd and ends that won't help you much against decent level foes. Or you could turn into a giant turnip (sorry a Huge [plant] turnip) and lash enemies with your turniptian tendrils ;-) or something...
Anway, my rambling message is basically saying this: pegging the stat increase to one, fixed value, regardless of spell caster level is not likely to yield a useful spell at high levels. I agree with the removal of many of the abilities that the old shapechange granted (or I accept them as necessary), but I really think that these spells need to be scaled to account for caster level. So +x/level above X etc. I'd love to know how a storm giant (a 'huge' giant) can even lift a storm giant sized boulder with the paltry strenth boost (+8 to average wiz strength) granted by the spell, let alone toss it hundreds of feet. If the scaling was done correctly, the lower level spells could retain their existing power levels and the higher level ones would scale to the point where they could actually serve a purpose in combat (both physical and other attacks). And if you are going to insist on the hard wired stat - make it the stat for a typical example of that type e.g. Huge Dragon (set the strength 30 etc, don't give a bonus. Or give a bonus that will take average caster to to average strength etc).