I hate to say it, but the RIFTS world isn't even that cool. I mean, the original idea isn't a bad one - a huge fantasy mixing pot - but it just got blown up with stupid, comic book-y stuff, which was fine... but it would then say "you could be the only guy with a mega laser within a hundred miles", which the game did nothing to reinforce.
The worst part about RIFTs is that, even if you use just a core-rules game, with none of the expansions, you will have a party where at least one player feels useless and at least one player just dominates. I've been in games where the Rogue Teacher (me) sat around and did next to nothing while the glitter boy destroyed everything in sight, and the wilderness scout made some rolls to get us to the next fight, and then repeat. And when we got to a city so I could be all Rogue Teacher-y.... the other two players complained that they had nothing to do, and the encounter got waved by - because, at least in those combats, I could shoot my pistol for 1d6 MDC or whatever.
That's RIFTS.
The best part are those where Siembieda talks about system rules and stuff, and acts like an expert. And he talks down all other systems out there for being unrealistic or whatever. Hell, most of the game books consist of Siembieda talking from down on high. Seriously, I read those books and it always feels like the author is talking down to me.
D&D has faults, but comparing the two is a lot like comparing the XBOX 360 to, say, Atari. Sure, Atari did some crazy and creative things in its time, and it looks great when looked at in regards to the times, but if someone released an atari today, it'd be laughed off the streets.
The thing is, RIFTS is the atari... it's still getting released, with no updates.