Or you could say humans have obvious Wookiee traits. Seriously though, I'd posit that he has very *subtle* human traits that we only recognize due to our tendency to anthropomorphize. No one would accidentally mistake him for a human - that's all I was saying.
That being said, I agree with you 100% about brilliant Mayhew's performance, as he completely brought Chewbacca to life. I'd also credit Ben Burtt with his magnificent sound design as well. I loved how you could always clearly understand what he was actually saying or feeling simply through his performance and the vocalizations. Frankly, I think saying that an actor *needs* his entire face visible is selling short the best actors, like Mayhew, who have performed amazing roles with mostly body language, or through a terribly restrictive mask.
My favorite two Chewie scenes: Alone in the Cloud City detention cell / repairing C3PO, and meeting up with Han in the cell under Jabba's palace.