by "humanoid" I'm assuming you mean human in size, shape, appearance... because that term usually covers anything resembling a human... like orcs, elves, dwarves, etc...
that said, it would be interesting to play as some of the roboty types, like a droid or something.
though, now that I think about it, the only mmo game that comes to mind that you can truly play a non-humanoid was Allods Online where you could play as some kind of weird fuzzball critter thing.