Höhlenwelt Saga is one of those games that gives you a limited resource of something (money, in this case) and makes you figure out ways of acquiring more, or optimize your path such that you never run out. I never found out what happens if you do run out, but since you need to park your flying dragon for 3 credits every single time you land it somewhere, and go through the same inane "here's my dragon"/"can I have my dragon back" dialogue every single time, I would suspect you're screwed if you don't
read about more ways to make money in the walkthrough find out what to sell to whom in order to make more money BEFORE you run out.
The plot? You're this space traveller who met his true love, but then she ran off with this other guy, so you're trying to track her down. And then the other guy, Cal, turns out to be a robotic savior of some kind, and directs you to the titular Cave World, which is a world that's part fantasy, part sf (you have alien invaders with advanced technology, but also dragons and magic). The author of the game was an acclaimed German fantasy writer, and used to write text adventures, so the world works pretty well for the most part, although there are some baffling things the protagonist can get away with, like: throwing pies in alien soldiers' faces; throwing exploding stink mushrooms at alien soldiers; and other insolence.
The way dialog trees are implemented is also somewhat bizarre: you can keep looping around until you happen upon the correct line of reasoning to get information (or someone to do something for you). This despite the game claiming that your dialog choices can have longer-lasting effects on the game (they don't). Furthermore, apparently "How is business, kind Sir?" will get you a tongue-lashing from a businessman, while "Heidau, dude, whassup yo?" will not. Ooo-kay.
Also interesting but slightly creepy is your "true love"'s reaction to seeing you -- she mostly remains coldly indifferent, sometimes even hostile, throughout, until the very end where you can coax her into a kiss with the right choice of dialog. And the main character will happily flirt with any other moderately attractive woman in the game, so there must be something I'm not getting here. Or the author.
So you travel around the place collecting stuff. Sometimes, you go back to the same place only to find new stuff there, and the protagonist even comments on this. Note to game authors: this is lame.
And, of course, while you manage to achieve the goal of this game, it ends on a cliffhanger that was never resolved. Apparently, so do the novels, since the author died mid-series, and wasn't famous enough to get Brandon Sanderson to complete it.
Overall, however: not a bad game. Too bad it's German-only and most of my audience won't get to play it.