I have a big green egg, and it is worth it. There is so much more to the egg than what has been said here. My favorite thing is actually to use it as a pizza oven. Baking a pizza at 600 degrees in 5 minutes is the way pizza is supposed to be. Crust will be amazing flavors of ingredients are so sharp and not blended together.
Also, the egg will get to temps that you can't get with other grills. For those that like steaks rare, or medium rare, you can sear a steak at 700 degrees for less than a minute and have the best you've ever had. Fish is better on the egg because it cooks much more evenly to prevent drying out.
Lifetime warranty is what separates the egg from other similar cookers like primo, kamoto joe etc.
I have the large and I can smoke enough food for the neighborhood, 4 butts, 6 beer can chickens, 2 turkeys. The egg being ceramic heats evenly and prevents any moisture loss. I've smoked butts low and slow for over 14 hours without adjusting temp control or adding charcoal. Set it up, go to bed and wake up to perfect smoked butts.
Because it fires up so easy, as opposed to big smokers, you will find yourself adding smoke to other dishes, chilli, soups, baked bread, biscuits, etc.
And of course burgers, dogs, etc are fine too.
It is kinda cultish though (like AU football). Check out the egghead forum and see what they do with their eggs.
http://eggheadforum.com/