First steam game?

That's a hard question, I guess a lot of people might have started with CSGO.

idk must be csgo or garrys mod

My first game steam was CSGO, really good game

My very first steam game was Counter-Strike: Condition Zero.

Probably Left 4 dead 2, one of the cheapest game out there and one of the best

i'm sure at 100% robot craft was my fist ever game on steam

Call of Duty Black Ops III

? , Garry's mod , Counter Strike Source ,
,

My first owner game on Steam is half life 2

Definitely still Garrys mod. It gets you passed the 5$ account activation and there is a TONE of content. Even today there are always new mods and content added by players.