It's not a tower defense clone. They added some constraints (no lateral movement) and removed others (no upgrades, set list of "towers" per game) which makes it more addictive.
They've obviously spent a lot of work tuning the game fundamentals and then added a great cute theme/graphics.
I think you are missing how important details are. This is why game designers for both board and video games spend months tuning their game mechanics to get it just so.
This is why Sid Meier games have his name on them and tend to be very popular.
It has a cute little story and the design is simple and intuitive.
I played through the whole game in a matter of days and I still wanted more. They must have got something right that Tower Defense and it's clones missed.
Agreed, I've never been able to get into Tower Defense games but I (and my 3 year old, to the chagrin of my wife) have really enjoyed playing this one.
As someone from Europe, I never really quite understood America's fascination with zombies: endless zombie movie films, semi-serious discussion about what to do when the "Zombie Apocalypse" hits, .... Care to enlighten me?
I could speculate wildly. Zombie films play on fear of death/disease, and the fear of someone you know trying to kill you -- or you having to kill them. I don't see anything peculiarly American about those themes though; I'd imagine they're pretty universal.
Zombies also represent the fear of something that looks almost human, but is not, and which outnumber you. That resonates with xenophobia (we're outnumbered, they're not human, and they work for $3 a day!) or pure selfish narcissism (I am the only "real" person, everyone else is an automaton / homunculus.)
There are also market forces at play - you can shoot dozens of them in the head and still get a "teen" rating for your movie or video game.
I'd love to hear other theories.
EDIT: Thought of another one. The "zombie apocalypse" shows the breakdown of civilization, and makes us realize that it's only goodwill that keeps society running. Our picture windows, screen doors, and windshields are only "polite" barriers that anyone could break through in an instant if they discarded civilized values. Maybe we (America) fear the end of empire, and are obsessed with what it might look like?
They've obviously spent a lot of work tuning the game fundamentals and then added a great cute theme/graphics.
I think you are missing how important details are. This is why game designers for both board and video games spend months tuning their game mechanics to get it just so.
This is why Sid Meier games have his name on them and tend to be very popular.