The classic shooter that revolutionized the genre and remains unmatched in many areas.
BAD: Not enough music; repetitive scientist models; level design gets a little weird on alien world
Half-Life is THE shooter game. Half-Life was the first game that made shooters what they are today. It redefined the genre, and to this day many of the elements you see in a shooter can be traced directly to Half-Life.
The campaign begins as just a normal day at work. Gordon Freeman is a scientist working on some top-secret scientific experiment of some sort that goes wrong and opens a portal to an alien world, who begin invading. So the plotline is unoriginal? That's the only thing. The game throws you out into a normal setting simply so it can set up the atmosphere of the game to come. This was perhaps the first shooter that ever attempted to set you up in this way, and in any shooter that does this now...the root of that was, indeed, Half-Life.
The atmosphere. That is what defines this game. The atmosphere is immersive. The first time a headcrab jumps out at you from a dark vent (of which there are many), it will certainly freak you out. I know it did me. The scripted events that go on around you are executed brilliantly, and this is what really fuels the immersive atmosphere. The game features nothing but short loading breaks to interrupt the action, and there are no cutscenes to see a different point of view. You see everything through Freeman's eyes and there are no levels in a sense of the word, another concept that has been heavily utilized by other games. Conveniently, Freeman never says a word, but you can understand everything that's going on by what other characters say and what goes on around you.
One of the greatest things about the campaign though was its ingenuity. Clever puzzles, extremely intelligent and top-notch level design (nearly unmatched even today), and astonishing, unmatched presentation all simply serve to fuel the realistic atmosphere of the game.
Half-Life's great level design takes you through a large variety of different settings, and the pacing ranges from methodical, careful progress to non-stop combat meshing beautifully with the level design. The pacing never seems to drag along too slowly or too quickly. No amount of words can explain the ingenuity of the level design. Half-Life was also the first shooter that did not place powerups, ammo, and health at random places. It was even the first one that didn't feature powerups of any source. All ammo and health will be found in storage lockers, shelves, and on the bodies of dead people.
Even for this day in age, the AI is fairly intelligent. The first time you encounter a large marine squad, you will be amazed at how intelligently they work together. For a game made in 1998, it's amazing that they even had the technology to create this clever.
Another great aspect of the game is the puzzles. The puzzles are never overly intimidating or frustrating, but are challenging enough to keep you entertained and are meshed smoothly with the combat and hallway-roaming (of which there is little true hallway-roaming). The puzzles are creative, intelligently-designed, and sometimes just plain massive (the part of Surface Tension where you must dodge tripwires to avoid setting off a massively mined storage facility for a nuke comes to mind). Another brilliant concept of the game are the aliens. The aliens are believable, creative, unique, and thoughtful and could fit in perfectly in a science fiction or fantasy story.
The sounds of the game are at least believable and realistic, and what little voice acting and music there is is generally good enough to keep me entertained. The graphics were groundbreaking for 1998, but definitely look outdated now.
However, despite all that is good about the game, no game can be perfect. There is only one type of marine and a handful of separate scientists, and it gets fairly repetitive after a while fighting seeing the same types of people over and over again. The level design near the end, especially on the alien world of Xen, is just plain weird, although I still found it creative, since you essentially delve straight into the innerworkings of the alien empire and they did about as good a job as you can on a completely alien society. In addition, the storyline is relatively cliched and has little depth to it (although the continued mysteriousness of the G-Man that continues into the sequel still intrigues me).
Overall Half-Life is simply a classic, atmosphere-driven game that's sure to remain a classic for as long as computer games exist. The presentation, artificial intelligence, revolutionary level design, clever puzzles, unique aliens, variety of settings, and perfect pacing are nearly unmatched, even in today's gaming world.