When I first started playing this game, I got addicted very fast. The art, music, and gameplay are phenomenal. I especially enjoy the squad like aspect of moving through levels and the micromanaging that this game requires. I also like that outside of missions, squads can devote their time to building useful equipment. I do have some complaints with this game though.
The first is that the game can still use some balancing. I say this because when I first started playing the game, I would try to build things that would increase the likelihood that I would get supplies. Each time I took this approach, I never made it past day 8. It wasn't until I neglected the upgrading altogether that I made much more progress throughout the game. I also feel that the 'chance' that supplies are produced for each upgrade can be improved a bit. Simple heuristic fix.
The second thing that bothered me was the absence of tutorials to guide new players along the game. The very first time I played the game, I thought it was strange that when I looked for missions I only saw one area (which was the base). This influenced me to stay in the base and keep upgrading until hopefully a new mission would open up. I later learned that it is required to replay the base level before you can advance...why? But more importantly, this is something that can easily be prompted to the player or removed altogether. Another thing on this topic is the fact that (I believe) you need to defend your base, meaning that you must clean out zombies occasionally at your base location. On one of my run throughs, I was doing very well until I suddenly died. I spent too much time upgrading at another region, but when I died I wasn't notified of how or why (so to be honest I'm still unsure if this is the reason why).
Lastly (and this is just my personal preference) I think I would like the game more if it wasn't high score based but more of a continuous progression. Meaning, I think that it would be better if each day created a save slot that you could go back to in case you die instead of starting the game over.
Altogether great game that despite my frustrations, kept me coming back for more. If this criteria of guidelines was evaluated, I think the game would be much better.