Here's a link to the physical game's entry over at BGG: Zombies!!!
Just played a round of the iOS version. It is fun enough, and the developers have taken an ambitious path rather than slavishly copy the appearance of the physical game, but it is still very, very rough around the edges right now (hence the limited launch, I assume). The most noticeable issue is that the graphics are currently hugely low-res and blurry, and a number of the interface elements (such as the round summary screen) are clearly half-finished placeholders.
Other than the current low-res art, I'm very impressed with what they've done on the visual side of things; instead using flat, bleak gray tiles to construct the city, the game employs chunky 3D buildings and structures that have a very appealing Tim Burton/Tim Schafer neon-Halloween aesthetic going on. Players and zombies alike have little bases attached to their feet so that they resemble the actual pieces from the game, and they stagger, shuffle and hop around the city on these.
Combat and construction are accompanied by dynamic split-screen animations that bring the game to life in a way it would have been easy not to bother with in a more straightforward adaptation. The event cards you play all draw on the artwork from the actual game, and are only let down by the same low-res graphics issue.
The core of the game is intact, and handled very well, with a number of gameplay options (standard rules, pre-populated city, quick play, and "survival horror"). You can play with up to four opponents, both live and AI; any game you play you can save in the middle, and pick up again later from a list of saved games.
The game does boast a couple of the best best design decisions I've seen in a while: the ability to fast-forward through pretty much every animation and even skip viewing an AI character's turn entirely if you don't want to watch it, and the ability to have the computer automate all the zombie/item placement and zombie movement via a single button press if you're in a situation where you don't need to manually handle these elements.
I didn't really intend to get into detail with this post and there's a lot I'm leaving out, but I'd suggest keeping an eye on this app if you like solid digital boardgames or are a fan of the original physical game. I just hope the developers can prettify the graphics and get them high-res before the game goes worldwide.