SAS 4 is an action game in 2D with a top-down view, where you have to face zombies to save people, find a vaccine, etc. You have to kill zombies with guns and armor that you can have by opening boxes (strongbox) dropped by zombies in-game.
You can buy upgrades for your guns & armors depending of the number of slot and the grade of them (normal max slots are 3 for weapon and 2 for armor, with a max of 10 grades per slot).
The game has 3 types of characters:

• The assault class, he’ the most powerful and the fastest one by its class skills; he can summon a group of 3-4 SAS fighters and he can lend a knife.
• The medic class, he’s obviously the class that can heal any players by dropping “medic kit”; he can drop chemical grenades.
• The Heavy class, he’s the most resistant one by its class skills; he can call an orbital strike and he can became almost invincible for ~4 secs.

In this game, you can level up by killing zombies or doing some missions (contracts) up to the level 100, it’s a big investment of time to “finish” the game without hacking, and for each level you get a skill point to spend and 100hp.

This game has a good amount of guns and amours, in 3 variants: in “normal”, in “[RED]” and in “[BLACK]”. Red and Black equipment are dropped in later levels.
The game has also several zombies, with 4 variants (2 for zombies “bosses”).
The main drawback is that the game isn't really balanced, along with “trollbox” or fighting against too powerful zombies...
There are bugs and other crashes that made the game needed to be refreshed between 2 and 5 games.

This game is overall great and "wealthy" (like some premium articles like a premium gun at ~40$). However, the game suffers of crashes, bugs, etc. It's a great flash game, but a prototype with Unity would be interesting