Nice game!
First of all, idea is soo unusual for me. Use of theme is awesome, really liked it! Everything feels nice and robust, except for digging animation, at the end there are strange frames that look pretty strange, but mechanic is working nice!
Didn't understand what purpose of zombies, to make you move around location? Feels, like there could be more, there is freedom for strategies, you can add some layer of gameplay by making zombies more interesting! They are just to simple for me, i think.
But it doesn't say that game is boring! Had fun running around location and digging graves, had that precious sense of wonder, maybe there is graves, maybe i can get somewhere high. You have a lot of opportunities to improve your game and make it really fun and interesting experience!
May add some variety to graves, like empty, or rare, or just some that can spawn the enemy!
Overall, great game! hope to see your other projects in the future!