There are tons of First Person Shooter (FPS) games now available on Mac but SHADOWGUN: Deadzone is one of the better free offerings. Although like many games, it's enhanced by In-App purchases, the free version is good enough to keep you coming back for more.
Death-match and Zone Control modes
There's a tutorial at the beginning of the game which gives you the basic controls - i.e. WASD to move around and use the mouse button to shoot. Press R to reload. You can select to join an online game and you will be "Spawned" into a World within less than 5-10 seconds.
In Death-match mode, it's just a simple case of shoot-to-kill or be killed. Depending on how many you kill in 5 minutes, you will be ranked in the SHADOWGUN: DeadZone leaderboard. At first, you'll get shot to bits very quickly unless you're a natural at FPS games. However, once you've got the hang of hiding behind things and blowing other online opponents away, the game becomes quite addictive. The weapons you have are very limited.
There is one grenade if you need it but annoyingly you can only upgrade weapons by upgrading to the Premium version. You can buy Gold via a Casino - you basically play on a one-armed bandit machine and depending on what you win, you can increase weaponry by adding real cash to your winnings and purchasing weaponry online. Zone Control mode sees you and a team protect your zone from enemy invasion but isn't as fun as Death-Match.
Decent graphics, sound and soundtrack
The overall sound effects and graphics in SHADOWGUN: DeadZone are pretty good considering it is free to play. The movement of players is realistic although the Death Match scenario gets a bit boring after a while - it would be nice to see more battlegrounds added.