Portal is the only one that doesn't need a third game. The second one ends with an actual conclusion and not a cliff hanger (HL3, the ending of L4D and the Green Flu, the final TF2 comic, ect.)

i have a theory: half-life 2 ep 1 and 2 are the third game splited in two parts cuz they where lazy

does back for blood count as L4D3?

No. For Valve it's a duology.

Just completed HL2 E2, now I am sitting here crying like a baby and there is no HL3 or HL2 EP3, I think I will keep crying.

no, episode 1 is a DLC, which means its not a full game.

HALF LIFE EPISODE 1 IS THE THIRD PART IDIOTS

counter strike

@HRT Operator nah, alyx is HL2: episode 2.5

half life 3 its hl2 ep3 try that mod