Marauder concept
Took a few minutes to think about a possible implementation of a feral shifter class, and came up some proof-of-concept stuff for powers. I think the selection indicates the general direction it could go in and stay 4e-ish. The main point is that I don't think the specific forms are your fundamental powers, rather that (at least for this particular example, which is specifically based around shifting, as opposed to a druid who has it as one of several abilities) they enable other at-will, encounter or daily abilities.
Harry
Marauder Attack 1
You make sudden, distracting attacks at the enemy's face and sides, creating an opportunity for your ally to dart in.
At-Will ✦ Primal, Weapon or Form
Standard Action
Melee attack range
Target: One creature
Attack: Dexterity vs. Reflex
Hit: 1[W] + Dexterity modifier damage, and the target grants combat advantage to one ally adjacent to it until the end of your next turn.
Menace
Marauder Attack 1
The target jumps back from your snarling lunge, unable to take its eyes off you.
At-Will ✦ Primal, Charm, Form
Standard Action
Melee attack range
Requirement: You can only use this power in hunter aspect.
Target: One creature
Attack: Charisma vs. Will
Hit: Dexterity modifier damage, push the target 1 space, and mark the target until the end of your next turn. A marked target takes a -2 penalty to any attack that does not include you as a target. A creature can have only one mark at a time, and a new mark supersedes a previous one.
Primal Form: Hunter Aspect
Marauder Feature
Your eyes suddenly shine back the torchlight as fur bristles from your skin and your fangs reach out for unguarded flesh.
Encounter ✦ Primal, Shapechange
Special: You can use hunter aspect, predator aspect or elemental aspect once per encounter, but not two or more of these in the same encounter.
Minor Action
Personal
Effect: You assume the form of a hunting animal of your own size, such as a wolf, jaguar or serpent. Your melee basic attack becomes a Dexterity vs. AC attack that deals 1d8 + Strength modifier damage (adjusted for size if you are smaller or larger than medium). You remain in this form until the encounter ends or you use a minor action to return to your natural form, which ends the power.
Hamstring
Marauder Attack 1
You tear at your target's leg tendons, ripping away at its ability to walk.
Encounter ✦ Primal, Form
Requirement: You can only use this power in hunter aspect.
Standard Action
Melee attack range
Attack: Dexterity vs. Reflex
Hit: 1[W] + Dexterity modifier damage, and the target is slowed (save ends).
Go for the Throat!
Marauder Attack 1
You leap on your prey, tearing away at a vital weak spot.
Daily ✦ Primal, Form
Requirement: You can only use this power in hunter aspect.
Standard Action
Melee attack range
Target: One creature
Special: You can shift 1 square before making your attack.
Attack: Strength vs. AC
Hit: 2[W] + Strength modifier damage, and the target is knocked prone and takes ongoing damage equal to 5 + your Strength modifier (save ends).
Miss: 1[W] + Strength modifier damage.
As far as things like flying around as a crow or hawk, I think those would mostly fall under the heading of "class features" rather than powers, since they would primarily happen out of combat. The ability to fly would probably be something you had access to around 11th level, judging from all the bits I've gleaned here and there.