I have played HL1 and HL 2 and I still have like 5 more in my backlog. I have no idea what HL 2 Episode 1 and 2 are, Black Mesa is just HL1 HD I think, Deathmatch is multiplayer I think, Deathmatch: Source is in my library too whatever that is, Alyx exists but is only VR I think...
Idk I got into half life thinking I had 2 games to play and now I have no idea what these other games in my library are. Going to have to do a deep dive soon.
Thats...gonna be hard. Unless you want a prequel, which I don't see how that would work. (The reason it wouldnt work is cause Chell is some time in the future cause of how long she slept)
I always hoped for a cross over game between HL and portal. You can play either Alyx or Chell, solo or co-op. Game evolves around you solving puzzles with the gravity gun and portal gun.