I've been thinking about how easily amused you'd have to be to get excited about yet another zombie-related game, and my conclusion is "Reddit poster who thinks rage comics and the same tired pictures with impact font on them are the height of entertainment".
This statement is about as intelligent as the statement: "I've been thinking about how easily amused you'd have to be to get excited about yet another 2D shooter game, and my conclusion is "weeaboos who love loli hentai." For all I care, ZombiU could have been RoboticaU. Most people's interest in the game stems from the use of the controller. Because, you know, when a system has a gimmicky/new type controller, people generally, you know, want to play games that show off what said controller can do. ZombiU is an example of what a FPS can do using the WiiU controller. I doubt many people would have cared if it was a FPS using zombies, robots, cowboys, ninjas, or mutant tacos. That's not to say I think it'll be GOTY, but will it be an interesting launch title to play? Absolutely.
Ironically, most Cave games this gen are practically excuses to draw little anime girls. The thing about zombies is, unlike the other things you mentioned, that not only is the concept extremely tired and played out, but as enemies they are very limiting, since developers mostly just stick to the same old tropes. A zombie that walks towards you slowly, then grabs hold of you and you have to tap a button to get free? Well, I certainly haven't seen that a zillion times already!
Again, the interest in ZombiU isn't from it being a zombie game, but from how it implements the Wii U Game pad. If that implementation underwhelms, the game will suck. If the implementation is neat, then it's worth playing regardless of the type of enemy.
I don't think graphics are really gonna get much better, at least I don't think there's much of a point improving them really. I like Nintendo's style, playstation and x-box are competing with each other over the same types of games but Nintendo makes games that are a lot different, sure some jerks think playing it means you don't qualify as a gamer or whatever but Nintendo will always have a place in my heart. They just make more memorable games in my opinion. If I had money I'd get a Wii U, unfortunately I struggle to afford food these days and I don't have a TV anymore.