I've just finished playing Half-Life (or in fact, the fan-made remake Black Mesa), and Half-Life: Uplink (the demo version that was released after the final game, and it consisted of a short non-canon scenario that's not included in the final game, but lately was included in the 25th anniversary version).

I will be playing HL: Opposing Force and Blue Shift next. And in general I am planning to fish every Half-Life game this month (except Alyx since I don't have good enough hardware for me to enjoy it, and playing it on GTX 1060 3GB is not enjoyable at all), and if it goes well Portal games as well.