Ok, the title is a bit over dramatic, but this is truly a great game. It really deserved the 50+ game of the year awards it received, and if it was released this year instead of in 1999 it would probably still get game of the year. Why? Because it truly immerses you into the game world, instead of just playing a game.

The first five minutes of the game was amazing the first time I watched it. At first I thought it was just an opening movie, so I was watching it. After about a minute, I accidentally hit the mouse, and I was looking at the ground. At that moment, I knew this game was going to be amazing. I realized that this was not a movie, but the game itself. Sure, after going through the beginning a couple of times, it gets boring, but that first time it is amazing.

Graphics

Even by today's standard, these graphics are excellent, while a little below the quality of maybe Quake III. The biggest complaint is the lack of a variety of models. There are 2 or 3 different scientist models, and it gets annoying looking at the same person over and over. Also there is only one model for the security guard, so it looks as though Black Mesa was only hiring people with that exact look.
Overall: 9/10

Sound

What?! They used sound for something other than just sound effects? Valve did something that had not been done much in the past, and added voices to what people were saying, and made it important that you listen to what's going on around you. I remember one time, I jumped around a corner, saw two soldiers and jumped back. I then heard "Fire in the hole!" shortly followed by "Oh SH*T!" When I went around the corner, all that was left was blood. I congratulate Valve for using sound for more than it has been used in the past for. The voice acting is fairly good as well.
Overall 9/10

Gameplay

Sure, the game looks great and has great sound, but does it play well? I answer that with a resounding YES! I have never had as much fun on any game as I have with Half-Life. The scripted sequences make you feel like you're actually in that world, and it's not all pre-programmed. They show you evidence of the outside world, so you feel like things are happening in other areas besides where you are. No other game has immersed me into their game as much as Half-Life. The game can be challenging, but it is not overly hard, and there are some funny moments. The AI is brilliant, and you feel like you are fighting against real, thinking people.
Overall: 10/10

Replay Value/Multiplayer

This game was really fun to play over again, but alternate ways to beat a certain area would have made it a little more fun. The multiplayer on this game is like an entirely different game. The deathmatch was nothing amazing, but when TFC came out, I played that for days at a time. The mod support of Half-Life makes multiplayer limitless. There are hundreds of mods out there for you to choose from, so you can choose what type of multiplayer game you wish to play.
Overall: 10/10

Recommended: Yes