Okay, maybe it's not my FAVORITE card, but I have come to appreciate it a lot more lately.
The thing about Gravity is it's so versatile. Use it to make someone land on your leveled-up Griffon/Gremlin/Gooba/whatever. Use it to cancel an opponent's Haste or even Anti-Magic (this works). Use it to get rid of a Silence or Waste that's been slapped on you, or to land on a fort/castle/empty leveled-up land (hey, it happens). In a four-player game I can usually get two or three good effects out of one Gravity if I time it right.
I'm toying with the idea of a Mine/Fountain deck with a lot of Gravities. Has anyone already tried this?