I'm really happy with the Adaptive Shifter. It's got the flexibility that I wanted from the main class, and I *love* the Reactive Form ability. The only downside of it is the reduced time for Wild Shape and late entry. I'm not really sure why that was necessary, but if the Archetype were strictly better than the base class I suppose that would be a problem.
I'm helping one of the people in my group stat one up right now, he's taking a Druid's Vestment to help with that particular limitation. We seem to think that the Vestment will just add another hour to his total usage, going by the wording between Unfettered Wild Shape and the Vestment.
Overall I think this is a marked improvement over the base class, but the delayed access to Wild Shape hurts as it means fewer overall Wild Shape feats (since you lose the level 5 slot).
I still can't understand why the Shifter can't be better at Wild Shape than a Druid.