If you think back to the 80s, was there a game you played without really knowing what the goal was?
One of the weirdest games I ever played - simply because I had no clue what was going on back in the day - was Wizball (Sensible Software, 1987). So many times my brother and I just started it, over and over again, never really grasping the concept. Only many years later (and finally understanding it) I have it another try, and what a game it is!
The concept is pretty nuts: In the once colourful realms of Wizworld, where the evil Zark has stolen all the colour, making it dull and grey. It is up to Wiz and his cat Nifta to restore it to its former brilliance as Wizball and Catellite. Ok then, let's go!
Design and music/sound were stunning though, which is why we still played it even when we didn't have the slightest clue what to do.