If you’re looking for a good old first person shooter which is also totally free, you should definitely play Black Mesa.
Black Mesa is supposedly a mod for the Source SKD 2007 engine, the engine which was used to create Half Life 2. Since Half Life 1 is getting quite old for today’s standards (it looks a lot like Doom) a group of modders decided to recreate the original game for the new advanced game engine with new graphics, sounds and music. Do not be fooled by the mod tag. This is a fully professional remake and it will keep you playing for many hours. As its makers claim it should be noted that the project is being built from the ground up and is not a simple port of Half Life maps and models into the Source Engine.
You control Gordon Freeman, a PhD MIT graduate working at the Black Mesa Research Facility. One day which seemed like any other you are given the task to place a non-usual sample of a strange material in the usual way into a device, after getting into your H.E.V suit. However, the sample material causes a “resonance cascade”, devastating the facility and creating an interdimensional rift to a world called Xen. That’s when all hell breaks loose.
The graphics are superb and I daresay they exceed in quality even those in Half Life 2. Valve must be jealous. Gameplay is exactly what you expect in a survival horror first person shooter type of game with the occasional puzzle here and there just so that you take a break from the heat of combat.
The game is about 3.7GB in size and requires Steam. Once launched from within Steam it will also prompt you to download the SDK before you can start playing.