Chrono Trigger because:

1.) It's a time-defying classic and

2.) It won't necessarily teach you "real-life skills" BUT it does make you think about time travel in general and some "time travel 101" issues, not quite so mind-draining as Steins;Gate but ... there are some things in life that literally can't be explained without resorting to either "time travel" or "aliens" or "we actually do live in a sim, in which case both time travel and aliens are possibilities"

A good runner up is the original MDK which came with the first Bondi Blue iMacs and the ending of which showcased just how far Apple COULD have taken video games (it starts out as "a bit underwhelming considering 1999 gaming graphics capabilities", then progressively gets more sophisticated in subtle gaming engine ways as you progress, and winds up with you literally traveling through a level which is basically HD video-quality open-heart surgery or something) had it not realized that dominating in the video games category would have made it susceptible to anti-trust claims.

Another good runner up is ONI which I believe may have been one of the first, if not the first game to be made available for the PS2 stateside.

It's playable with a keyboard but you'll want a controller.

Basically it's a combination of 3rd person shooter, stealth, respectably-advanced Tekken-like fighting game AND at one point close enough to the end it sort of becomes an exercise in Olympic gymnastics.

Ghost in the Shell is also a pretty cool ONI-like follow up that has some "surreal" levels that literally make you feel like you're actually in a post-apocalyptic pseudo-utopia Japan.

If you like immersive feels, you might want to try the .hack series, but you'll need the anime series as well to get the full "back-and-forth, in-and-out of different frames of reference" thing; unfortunately the corresponding websites with news elements, pseudo chats, etc. are long-gone.

Having said that, if you want a REAL trip of a game, I would highly recommend "Sumo" for the Mac.

I believe it's still available for free, as it was offered originally as a way to celebrate the developer's thesis in Ai.

When you first start playing it, it seems like it's an unfinished project; as you progress through the levels (same thing basically over and over again: a sumo match with two marbles, using your mouse to "push" and the mouse key to "grab and hold" while you "pull") though it starts not only learning your approach but anticipating it as it eventually starts tossing it's own capabilities at you.

Levels 1-40 or so take anywhere from a few seconds to 30 seconds; levels 40-60 wind up taking half a minute to a few minute or more; levels 60-80 become ... "challenging" ...

Levels 80-90 become HARD ...

Levels 90-99 become EXPONENTIALLY HARD and by level 97-98 it can take you well over an hour to "defeat" your opponent ... but then whatever it is you did to defeat your opponent is rendered useless in the next level as the opposing marble sumo wrestler now anticipates that, too and starts doing so many things to trip up your approach ...

Let's just say when I played it, I got to level 99 and after about an hour and a half I "lost" when I fell off the pool-of-sweat-drenched computer table onto the floor with the mouse still in my hand, which wound up disconnecting from the computer (and let the Ai push my marble off the platform effortlessly).

I literally felt muscle aches throughout my body the next day, not unlike going to the gym and overdoing it.

I'm not sure I'd call Sumo a "fun" game like Chrono Trigger, MDK or ONI, but it was definitely an "interesting" experience ...

AND THEN of course there's "probably a reason" there have been, over the course of the decades since it came out, so many Deus Ex (original game) memes, including the "You don't have to reinstall Deus Ex if you never uninstall it" one.

This game came out before "auto-saving" and so you'll want to make quite a few save points in this RPG-like FPS/Splinter Cell-precursor or else you'll wind up stuck in a warehouse compound patrolled by Robocop-type automated security as well as the realization that your entire skill set tree, which was GREAT in getting you there, winds up being completely useless in getting you out of certain situations so ... yeah ... strategic use of save points.

Last but certainly not least is a PS1 game I got in the bargain bin for I think $1 called "Tale of the Sun" ... can't quite describe the perfect fusion of idiocy/zen-bliss the game routinely made me feel while playing it.

It's sort of like Grand Theft Auto: Vice City was like before all the "online" complications: you just come back from work/school/whatever, pop it in, and just feel ... like this perfect Zen "no-mind" bliss while wandering around, sorta doing quests, but not necessarily, sorta seems like you sorta know the layout, but the territory was both impossibly huge AND full of unexpected surprises, perfect mix of just wandering around in open fields, sorta Zelda Wind Walker like but much simpler, sometimes a wooly mammoth would find you and you either had to spend 20 minutes running away or 10-15 minutes fighting it ... just ... hard to explain the simple good feels this game made people feel.