Have You Played... Sin?
Or SiN, as was the style at the time.
Have You Played? is an endless stream of game recommendations. One a day, every day of the year, perhaps for all time.
Released on October 31st 1998, less than two weeks before the first Half-Life, Sin is an odd footnote in the first-person shooter's growth from carefree, violent romp towards the carefree, violent romps with scripted story bits they are today.
There's lots that's consequently old-fashioned about it, chief among them the awful, inflatable villain Elixis Sinclair. In the context of 1998 though, it was ambitious: it was one of the first FPS to have locational hit detection, so shooting enemies in the leg would cause them to limp; it had extremely destructible scenery, as tables and bookcases would crumble under fire from the still-satisfying shotgun; it had in-engine cutscenes (albeit rubbish ones), and in-game computer terminals, and at least some slight branching to its scripting.
Half-Life is the much better game, but it's also much more limited in scope and ambition by comparison. Sin was attempting to carry the ideas of Duke Nukem 3D forward, and while it's consequently crass and dumb in retrospect, there are still reasons to remember and play it today.