How about a game well worth paying for that's free for download?
The Ur-Quan Masters, a port of the old Star Control 2 for modern PC's. It's a single player RPG with a really good storyline, plenty of puzzles, tons of things for the player to do in addition to the essentials required to win, and multiple ways to do a lot of things. Also, unlike most CRPG's I know of where you can take however long you want to do anything with no consequences, when the aliens you talk to say time is running out,
they mean it.