Hm. Shapeshifting. It seemed like such an awesome ability, and then when you played it, it just wasn't.
Wulfrum: You might be right, in the sense that the game seemed to be trying to make a mage into a warrior. But none of the creatures you could become would be better armored or have better abilities than the enemies you'd be facing later on. The only way to make it useful, then, was to have the tree fully unlocked from the very early game and invest heavily in strength--after the early game it becomes useless.
I also think becoming corrupted creatures was a bit off kilter. If you aren't corrupt yourself, your forms shouldn't be (so that made sense for the Warden, but not for Morrigan). Plus, there was a very limited number of forms available.
Shapeshifting could be a lot more interesting if it didn't necessarily just make you into a warrior, but gave your mage other abilities that may or may not be useful in combat. For instance, become a cat or a squirrel for stealth, nothing notices you until the spell wears off or you end it. For poison and stealth, be a snake or a small spider. Spiders shouldn't be warriors. But if you want to be a warrior, turn into a bear. (It might be interesting if there could be armor made for your beast forms--then you could turn into a massive armored bear.) Or, maybe a halla. Higher level fighting abilities might mean taking the form of a drake or a dragonling. It would just depend what you needed to do. Unfortunately the game never seemed to treat it that way, and yet I can't help but believe that there was definitely some purpose to using the animals they did. But no one ever seemed to do well with any of them, so... Your guess is as good as mine.