I actually like where you are going with it.
One quick question: I do not see an Alter Self-like ability for the metabolist. Seems to be a good moderately low level ability for them.
I have tried a few playtest sessions (just two of us, so not a lot of group action unfortunately). I like the overall feel of each of the sub classes. I do think that they seem a tad underpowered at times. Again, however, this may be from lack of a group dynamic in our playtests.