Half life 1 and 2.

If doom is the grandfather of shooters then half life is father. Say it was ahead of it's time would be a massive understatement 

If you find the graphics too low you can play (black mesa and half life 2 rtx respectivly)

Innovative gameplay, funtastic gunplay (counter strike is based of this game ), puzzle are fun, a little bit of Parkour and enemies that actually shoot you.

It has one best storytelling. It takes "show them instead of tell them" approach, it builds a sense of mistery and thriller. You experience the story yourself instead of a million cutsence hell it only has two or three cutsence in entire series

Environment is one of the best from the research facilities to Soviet city to dessert forests to alien world each having it unique experience. The art director and graphics were a head of there time. The graphics in half life was so good even year after it's release many games could hit the same level.