I never played any of the other Far Cry games, but apparently this one is really different. I bought it from GS during a B2G1 sale, beat it in less than a week & took it back. I really enjoyed the single-player experience but there are a few things, and they're kind of major things, that take away from it being a great game. Still very fun to play & it looks awesome.
edit: For those wondering, the bad things about the game are that there aren't random people in the world. Well there are, but they all want to kill you. So you can't go anywhere without getting into firefights. And the other is that it takes forever to get anywhere. It's a big map, and there are fast-travel locations, but it seems that it'll take longer to use those than to head straight for your destination. Also, you start off the game with Malaria & have to take pills for it - kinda stupid if you ask me, but wasn't a big deal. Others, however, really hated that part.
But yeah, I'd wait on this game til ~$20.