Hl1 and hl2 are not really connected plotwise and can be enjoyed separately. There’s some small references and a couple characters you wouldn’t necessarily know even if you played HL1, because HL1 didn’t have much of a focus on that kind of story-telling.
The series is certainly a must play because of how much it influenced the industry. Going back to it now may not seem like it’s all that great; but you gotta keep in mind, it was one of the very first FPS games designed this way. Before Half-Life, FPS games were all just basically Doom clones.
No. They publicly stated the cancellation of episode 3 years ago when it was still relevant, and is one of the reasons I was always confused about every single rumor that HL3 was going to be a thing; they never announced a HL3 and they already said Episode 3 wasn’t coming out. Where the heck did the HL3 rumors come from?