Pros:

Has more than one path
Level design is similar to that of Minecraft
Really fun event at the place with the statue and the mossystone
Zombies BREAKING THROUGH THE BLOCKS!

Cons:

No music, custom sounds, etc.

Conclusion:

I love this a lot, and can't wait to see what you have for the future. I hope that you expand it beyond what it currently is(more maps). As well, a survival/scavenge map would be really cool and I would play it a lot.

Make a nether map, too! In the future, too, you should add custom models and stuff for zombies and survivors and weapons.