A little IMHO on Arma 2 and Dayz:
Arma 2 is not good. It's not that it couldn't be good, but the interface is horrid. If you are into military sims maybe you can get your mind around this and find it good, but when a game is a "simulator" which means you need to be precise, careful and can't get shot, clunky interfaces make the game miserable.
Those issues carry over into DayZ. This game is not a FPS, it is NOTHING like Left 4 Dead....I would say it's more like Theif or Assassins Creed in that you have to be quiet, hide, wait, sneak around etc. Again though, it is scarred by a horrid interface. Honestly, whoever made the Arma 2 interface is not a gamer...but then again, if it was made with the help of the military, they have a tendency to make things more complicated than they need to be.
That being said, DayZ is fun. It has moments as intense as Amnesia (or EvE Online) due to the gameplay and death you lose everything aspect. That is also kind of it's weakness. There is no real "goal" other than to live and living is tough. It is probably as close to how real life zombie apoc would actually be.
I will also go back and say it is like Eve Online in that you never know who your friends are or who will betray you, which to me adds to the excitement. It's not a game for everyone, it's not fast paced, and as mentioned it's still alpha, with plenty of bugs, server resets, and updates. It can be frustrating, but something about it overcomes all of that.
Sorry for the long post..