Completely different abilities.
Most transforms increase your hp and add Stability.
Rampage is pretty much just a bunch of CC abilities (your Physical War Utilities essentially), and Melandru is just supportive abilities.
Melandru is pretty friggin terrible TBH, just because all the abilities take forever for the animation to finish, but it has the 1200 aoe root ability which is nice, and you can always pop it on and off just to get the stability.
You can always test (non-racial) stuff in the Mists just so you know.