Back in the day (mid 1980's to early 1990's), we didn't have the luxury in choosing what to play as we have now.
People older than, say, age 25 probably remember what I'm talking about. 
Games were pirated all over, and usually, you wouldn't have a manual to your disposal.
As for most games, we didn't need any manual, because they would speak for themselves.
There were some games though, that seemed fascinating, but were more obscure in their workings.
Still, I kept playing them, as I liked the atmosphere, the graphics, the music... even if I wouldn't ever beat them (of even knew if they could be).
Do you recognize this? I'll give some examples - maybe you have some of your own.
Colony
Putting up fences, fending off the huge ants, placing the beacon, waiting for the ship...
It's probably quite some intricate gameplay, which was lost on me.
Cosa Nostra
Sometimes, you kill a corrupt politician or police man, and the game rewards you for that (and tells you in Spanish).
The point of the game, I never found out. I just wandered around and shot people.
Death Wish 3
I just would shoot everyone to hell until I ran out of weapons.
The map system and the telex at the bottom right of the screen -
Didn't understand. Loved the music, which was a great factor in commencing play.
Kubikiri Yakata Yori
Actually beaten this game a few times, because the graphics and music fascinated me so much.
Even if I could only understand like 20% (and that's generous) of the on-screen dialogue and menu choices.
It's a visual novel type of game, but you can actually die in this, and there's a genuine dead end mid-game (which seems strange).
Anyway, an exception on this list, since I've beaten it a few times - still on the list because I hardly understood anything of what was going on.
Sailor's Delight
Liked playing as a robot and the musical rendition of "Drunken Sailor", but the actual game mechanics were lost to me.
I guess... prevent your ship from flooding on the inside and sinking?
Spy vs Spy II
Cool setting, based on a cool comic. But what to do?
You seem to be supposed to trap and damage or kill the other guy, but I never found out how.
