Buggy. Also, It's been said before, but...
You honestly want us to pay for content in a flash game?
Anyway, one of the bugs I found was that after finishing survival mode, then going back to it form the main menu, it starts out with zombies already coming, at the same difficulty level they were before I died.
Also, I noticed that if a Zombie attacks a barricade (The barbed-wire ones, at least) after about 30 seconds it will disappear, no matter if a zombie was still attacking it or hadn't been attacking it since.
Thirdly, I was on story mode, hard difficulty, and Ellie had died just before the Prostitute came in. When the menu came up to decide whether or not to let her stay, I chose not to. And then the game froze with the buy/next round menu up. I could turn my character, but he couldn't move, and I none of the buttons would do anything.
"GamerSafe scoreboards, achievements and microtransactions are used to further increase the immersion."
This made me laugh. Achievement notices popping up mid-game, and having to leave the game to check scoreboards and pay for 'gamergold' do not increase immersion. Rather the opposite, in fact.