There are two expansions for the first one, Opposing Force and Blue Shift. These explore the same events, from the points of view of different characters.
After the second one there are also the two shorter, stand alone, stories, Episode One and Episode two. These continue the story from the point of view of the protagonist.
Half life, all of them, in order
There’s only 2 right? Exculding That VR version
There are two expansions for the first one, Opposing Force and Blue Shift. These explore the same events, from the points of view of different characters.
After the second one there are also the two shorter, stand alone, stories, Episode One and Episode two. These continue the story from the point of view of the protagonist.