There is not much to specify for the question, its really simple: Which title is the first game you have purchased on Steam? Was it a good decision? How much did you pay? When was it and what device? You don’t have to answer all questions, this is just a fun discussion to have.
You can check your history: https://store.steampowered.com/account/history/ Edit: Some in the comments pointed out that the purchase history doesn’t go back all to the beginnings of Steam. So if you purchased something earlier, it won’t be listed on your account.
(I reply with my game too.)
I remember having to leave my PC on overnight to download Batman!
My dial up would disconnect every night at like 2AM so that wasn’t even an option. I’d leave it and come back to it stopped entirely and it wanted to restart the download entirely anytime there was an interruption.