Expect the unexpected with Half-Life.
The premise of the game is simple: you are a researcher in a facility located in New Mexico called Black Mesa. The protagonist name is Gordon Freeman, a man you relate to very quickly. I don't intend to spoil anything so you can have the chance to be shocked since that is what the game is all about. The presentation of the game is simply fantastic. There are no introductory cut-scenes, you find out about what's going on in game so pay attention to your suorroundings. Don't get me wrong: since the start the story begins to lift up quick and that sense of knowing what happens is what keeps you excited to play. The game doesn't play in levels, rather than that, you advance through chapters indicated by their respective title that will load at the start of them. Don't expect HL to be only about shooting, there are also occasional puzzles to keep you busy and they're not as dumb as you think they might be.
Now, you'd probably think that this game is very dated for you to play. Let me tell you something: it is not. Despite almost being a 6 year old game (9 if you count when it was released on the PC), it's still one beautiful masterpiece that should not be missed by anyone. Don't let the old graphics fool you, they still look very good even for today's standards. And just one more thing: HL simply kicks ass.
Besides the single-player mode, which will keep you entertained for quite some time, there are two multi-player modes: a cooperative two-player mode called Decay that acts as another perspective of the HL story and the classic one on one deathmatch.
To wrap this up, the HL experience is one amazing ride that not many games accomplish. Indeed this game is one of the best, and for many different reasons, you, as the player, needs to discover such reasons. Go play HL now.