I don't think you can go wrong paying $6.95 at the Bundle of Holding to get hold of Robin D. Laws' Hillfolk and diverse series pitches from a weighty proportion of the skilled rpg writers in the world.
But you can go wrong if you wait more than twenty hours to take advantage of the offer. It ends tomorrow.
If you've been following Robin's games from The Dying Earth through Heroquest and Skullduggery, you know he's been on a quest for narrative roleplaying mechanics. Hillfolk is the culmination of the quest. Its expectations aren't like the procedural games I usually design and run, it's focused on stories about who wants what from whom and what the dramatic consequences will be, not who can slay who using which spells. It's certainly been good for my thinking to be involved with the game and its dramatic cousins, so if you've held off from dipping into Hillfolk because it's not the style of game you usually play, now is a good moment to experiment.