Well there is
Half Life 1 (HL1 Graphic) --> Black Mesa Source (HL2 Graphic)
Half Life Blue Shift (HL 1 Graphic) --> Guard Duty (HL2 Graphic)
Half Life Opposing Force (HL1 Graphic) --> Operation Black Mesa (HL2 Graphic)
Why not:
Half Life 2 (HL2 Graphic) --> [Name example: City 17] (HL1 Graphic) ?
Half Life 2 in GRAPHIC HL1 would be great huh? Sounds good huh?