Well, I'm giving this a thumbs up because I enjoyed it for a while, and only considering that I paid about 2,99 for a key, plus 3,99 for the Annual Pass on Steam.

The game does a lot of things right, but there are also things that aren’t really enjoyable.
Gameplay wise, it’s somehwat similar to L4D/L4D2, World War Z, Zombie Army 4, etc.

What I enjoyed about it were the level design, the graphics, some of the characters, the customization options, and the fact that the maps are long enough to fulfill my old Left 4 Dead needs.

Characters and zombie variations are not very creative, but they’re alright.

I had about 20 hours of fun with it before I lost interest for several reasons.
With a more active player base, I might have played more, but ~5 years after release, I may be a bit late to the party.

What I don’t like are some of the gameplay choices.

Instead of making it a smooth “just play and enjoy” style like the aforementioned L4D or L4D2, they added an annoying perk card system that tries to add some variation. In practice, tho, it just annoys me and feels out of place in this game.

When you finish an Act, you get thrown back to Fort Hope, aka your “base camp,” so you lose the lobby and have to invite people again. This is especially annoying because it takes ages to find enough players in a public match to fill the lobby.

That’s another point.
First of all, server connections take longer than I’d like, and then you’re mostly on your own with bots.
If you're lucky enough, you'll have three friends to play with right now, otherwise, you might end up waiting 10+ minutes for other random people to join.

I didn’t mind playing with bots alone and it’s entirely possible to complete the game with bots on Recruit or Veteran.

But is it fun?
Well, the first time through, when everything is new, yes.
But the second time, I really would have preferred to play with other people.

So you wait and wait and wait.
Then you finally get a full team, and I always had the issue that one person went AFK after one section.

You can’t directly kick this person either. Why? Who knows.
They will eventually be auto kicked after a while, but that takes way too long.
On higher difficulties, that’s extremely annoying.

The bots themselves are alright.
They kill a lot of enemies, share ammo, heal, and help you up, but they also get in the way a lot.
If I aim down sights to snipe or shoot a group of zombies with an assault rifle, after two or three shots, a bot will randomly run back and forth in front of my shots, almost as if they’re doing it on purpose.

I can confirm they did come back 4 blood and took it by force. 10/10 would definitely donate more blood for the cause.

If this game came out a few years later and not advertised as a L4D successor the reception to the game and it's card rougelite mechanics would have been much better received. It's a good game and more than playable solo and at it's best with a group of friends.