HalfLife's strength and staying power lie in its immersion: although HalfLife is thin on plot, its ambience and atmosphere are unparalleled. In a remarkable design choice that has been successfully duplicated only by the game's sequel (see below), the game takes great pains to avoid breaking your personal connection to Black Mesa. The 18 levels of the original game flow into each other seamlessly, with (but for a few story-related exceptions) no narrative breaks. Furthermore, while the game features a number of friendly characters with whom you can interact, Gordon has no dialogue--HalfLife forces no personality upon you as a protagonist, and GordonFreeman? becomes, in effect, the vessel of your own involvement in its story.
In addition, HalfLife has been popular for it's highly mod-able engine, which has given rise to the most popular multiplayer game of all time (CounterStrike) and the game of choice for weekly CrackInTheAC meetings (NaturalSelection). More recently, HalfLife has been replaced by the long-awaited HalfLifeII, with great graphics, extraordinary physics, and a return to the immersive atmosphere that made its predecessor an instant classic.