1998. HALF-LIFE sends a shock through the game industry with its combination of pounding action and continuous, immersive storytelling. Valve's debut title wins more than 50 game-of-the-year awards on its way to being named "Best PC Game Ever" by PC Gamer, and launches a franchise with more than eight million retail units sold...
Imo the best enjoyment to time ratio is:
Black Mesa (the Xen level at the end was redone and extended compared to in HL1 and it’s cool but if it starts to drag just move on)
HL2 (main game)
HL2: EP1 start it but maybe skip and watch a playthrough if you get bored
HL2: EP2
HL Alyx, if you can play it on a decent headset. DO NOT MOD IT TO PLAY IT WITH MOUSE/KB it will be extremely boring since it’s designed for VR
Have fun, there’s simply nothing else like Half-Life games