I have always had a love/hate relationship with Rifts. It represents a truly remarkable setting with enough elements to keep players returning to it for years (and still not exhaust the possibilities) married to probably one of the worst systems ever designed.
The Rifts setting is a post-apocalyptic Earth, ravaged by the arrival of Rifts, or tears in the fabric of reality which allow Dimensional Beings to intrude on Earth. Magic has returned in many wondrous and strange ways, giving you a chance to explore a post-apocalyptic/fantasy/sic-fi setting that easily incorporates elements of horror, high adventure and even Western genres. Whilst this might seem a little over the top, Rifts pulls it off with style. Even the prevailing propaganda-driven Coalition government, backed up by a military clad in death imagery is finely executed and integrated with a believable rationale for existing.
The big let down is a cumbersome, rules-heavy system that bogs every action down in multiple rolls and throws the concept of game balance out the window. A GM needs to be incredibly vigilant in this game to decide how to handle the insanely disparate power levels within a party, let alone when they begin adventuring.
Also, the GM and players need to be aware of the power creep that is evident in the supplements. As the publications were rolled out, there were a host of new OCCs and RCCs (think character classes) that ranged from the mundane to godlike in terms of the influence they can wield in a game. Likewise, the equipment suffered a similar power creep, that isn't always welcome.
On the positive, Rifts will allow you to mesh any genres together, and there will be a setting book for absolutely any taste in your group - but sometimes too much choice can be a bad thing. On the negative, you have an unbalanced, unwieldy system that is every power-gamers fantasy.
The choice is up to you, but I'd buy Rifts just for the ideas.