Our audience may skew towards us old fogeys who remember the days of DOS memory management. Some of you are still young, or just late to the party. The Ancestor Bundle over on Fanatical costs as much as a cup of coffee - cheap cafeteria stuff, not Starbucks - and gets you a bunch of immersive sims including both System Shock Games, Strife (the 90s one, not the MOBA) and the more recent Spirits of Xanadu. You also get dark point-and-click adventure I Have No Mouth, And I Must Scream, N64-era platform explore-o-shooter Shadow Man and recently re-released mech RTS Metal Fatigue.
The stars of the show here are undoubtedly the System Shock games. Both are classics of their time, and defined the immersive sim genre as we know it. Without System Shock we'd have no Dishonored, Deus Ex or Prey. Night Dive are currently remaking the first game, but gave its original DOS-era edition a bit of spit and polish just a few months ago. Intriguingly, System Shock has only just developed a mod scene, too. If you finish the game and want more to chew on, check out ReWired and Ruby Station, both on Mod DB and designed for easy use with the new version.
System Shock 2 aged better than the first. Some chunky character models aside (which can be replaced with more HD counterparts), it's up with the original Deus Ex as one of the best immersive sims out there. A huge infested spacecraft to explore, tons of weapons, skills and psionic powers to play around with, and mods if you're done with all that too. The biggest and most ambitious mod for it is System Shock Infinite, inspired by Bioshock Infinite's multiverse hopping. Lots of plot branches and alternate timelines to explore there, if you don't mind some awkward voice-acting.
Spirits Of Xanadu isn't an old game, compared to the rest here. Released just four years ago, it's a chunky low-poly tribute to System Shock. A spooky spacecraft overrun with killer robots, mad science gone awry, limited ammo and puzzles to solve. It's familiar immersive sim stuff, and sits nicely alongside the Shock games. A good example of the many games inspired by Looking Glass's originals over the years.
Strife puts shooting first and thinking second, but was arguably ahead of its time in many ways, and holds up pretty well now if you don't mind the occasional labyrinthine sewer level. Sharing a lot of code with the original Doom, it has fast, snappy combat and a fun comicbook post-apocalyptic world paired with branching dialogues and (in some cases) multiple mission solutions. This version is yet another remaster by Night Dive and includes a nice set of upgrades, including modern lighting, shadows and some fancier effects.
I Have No Mouth, And I Must Scream is "a horrible game, made up of horrible scenarios, populated with a handful of horrible people and horribly punishing to play through", according to former RPS boffin Adam Smith in his retrospective piece on it here. Despite its sadism, he had a good time returning to the bleak, cruel world of Harlan Ellison's novel-turned-adventure. You may need a guide to get through some of the more obtuse puzzles, but its journey through five metaphorical virtual nightmare-worlds is a trip. Not really my genre, but I'll vouch for its impact.
Shadow Man is a bit of an oddball. A quirky voodoo-themed action adventure that's equal parts unsettling and comically corny, or at least it was back when I first played it on the Dreamcast in 1999. It did the 'hopping between the world of the living and dead' thing a year before Legacy Of Kain: Soul Reaver, and doesn't handle it quite as elegantly, but it does have some clever ideas hidden away in there. One of the more awkward games to play in this bundle, though, even compared to the original System Shock.
Metal Fatigue is the odd one out of this bundle. Recently updated to play nicer with modern machines by Night Dive, it's a pretty standard early 2000s real-time strategy game. You build bases, churn out tanks, and the occasional giant psueudo-anime robot. These big humanoid weapons need to be assembled from two arms, a pair of legs and a torso each, and the components determine what they can do in combat. You can also steal fallen limbs from the battlefield and bodge together units from your dismembered foes, which I remember being rather satisfying.