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.)
Purchased myself or redeemed a code for?
I was gifted the orange box for Christmas and that’s when I registered my account. First actual purchase through steam was audiosurf but had redeemed Left 4 Dead and CS:S before that.
Technically my question is about when you decided yourself to buy a game on the Steam platform itself, to spent money on it. But I didn’t think everything through. Therefore, we are here to have fun, so the question can be understood a bit more loosely too.