A Must Play for all gamers!
The game has been a landmark for its AI, scripted sequences, and interaction with objects via the physics engine in the game.
Right from the beginning when you arrive at the "Area-51" type facility known as Black Mesa, you are coming to your first day of work as scientist Gordon Freeman. After having a good introduction to the gaming world and the types of characters you will come in contact with, that game forces you into a situation that makes you feel helpless as the facility around you collapses from an experiment gone wrong. You are then forced to become skilled at using weapons to overcome the challenges that await. This is a good chance for players of the sequel to see what happened previously if they didn't play the first game. This game is now a great bargain, with players having the choice to buy the second game and having this one come with it. Though this main character never talks much (like most main characters), I think that the game does a good job of putting you in "his shoes" and having to navigate through this vast world. There are no levels here. This is one of the first games to make best use of actually loading to the next area, while making you feel the whole world is one.
This is the first game that surprised me on AI. In the past I would know that all AI is, is just programming for the NPCs (non-player characters). "If the player moves there, I move here" ect. But this game freaked me out, making me think that the computer was actually thinking on its own. The enemies that made me feel that way was the human marines. The alien enemies don't have this same effect. They just have certain "instinctive" patterns to their behavior that you have to figure out in order to defeat them (which many force you to run for cover as quickly as possible because there is no way to dodge certain attacks).
I highly recommend giving this one a go, especially if you've played the second game.
The downside for modern gamers is that the graphics are obviously dated, but setting that aside for the gameplay in place, this game is an absolute masterpiece. Many mods have spawned off of this game's engine (source engine), which makes the game have great depth after you play the original campaigns.
Half-Life has had mods made after it, such as Counter Strike and Day of Defeat, which now have great success on their own. These two games now are enhanced with Half-Life 2's source engine, but the originals can be played as well.