I posted a mini-review over on Dakka before Christmas and this was one of my queries as well.
Not used Were Creatures yet, but I will say that Warbeasts are not a great choice for slogging across the board - they're too fragile to take many attacks, even with their good armour, and they fail a Move action on a 5- (or about 28% of the time).
So this system lets you take a full-Strength unit, only failing its move action 17% of the time (for many foot units). It can take hits as it moves. When it transforms, you get a unit of melee monsters (literally!), Strength refreshed, hopefully somewhere near where you want them.
It forces your opponent to consider that a 12" move unit hitting on 4+ with Wild Charge could descend on them next turn - your job is to give them an embarrassment of targets...
Roll every time a unit takes a hit, hide the results but be honest?
The activation economy in DR is pretty brutal - Were Creatures lets you play to unit strengths and give you a fresh unit after crossing the board. It does still seem overpriced, but I'd need to play it to see how it works in practice.