Your first point is flat-out wrong. CS had a degree of significance in HL's success, true, but TF was a quake mod first, and both only really hit the mainstream

Your first point is flat-out wrong. CS had a degree of significance in HL's success, true, but TF was a quake mod first, and both only really hit the mainstream when valve picked up the developers and made the games standalone. HL made its own legacy, and it's for a large part due to its mixture of story and gameplay. To paraphrase Yahtzee on the subject: "The thing you have to understand about half-life is that in most shooters at the time, guns still hovered three feet off the ground, spinning gently like Barber's poles, and nothing else had ever felt so absorbingly real"