"the buttons layout seemed unnatural (to far from each other and from the edge of the controller). It was kind of uncomfortable and I'm not sure I could shoot my way through multiples agressive zombies like that."
That's what concerns me when I look at the Wii U controller. The weight I could get used to, I play with a pillow on my lap, anyway, to support my hands, but the motion required to reach some of the buttons looks uncomfortable. Does ZombieU support the classic controller?
I wouldn't worry much about the graphical prowess of the launch games, though, I'm sure that will improve quickly.