This game takes you into its own world. It is like a combined version of survival, horror, and fps games. You can feel like you are playing Rust, Minecraft and Dying Light at the same time.
Every 6 days you have to loot the environment, strengthen your base and improve your tower defense because when the 7th day comes, the zombies will attack you hard. And every 7th days these attacks will be more difficult.
If you just want to enjoy the game without stress, grab your friend and play with the PvE mode.
The game is constantly evolving. Every Alpha release comes with real changes, which is nice. The graphics are not super but ok. The Shooting mechanism and gameplay are cool. The only problem is server issues. I hope they will fix it in the future.
Prepare for day 7 and if you are well prepared, it will be the hardest but most fun day ever.

PS (after A20 update): I highly recommend you to try this game with the A20 update. They fixed many server issues and improved graphics quality. They also improved construction dynamics and added new construction material shapes. The zombie world is definitely better now with the A20...