Amber, more than any other game I've ever played, relies totally on the GM to make the game good. As any conflict resolution basically comes down to the GM looking at the requisite stats, listening to what the players want to do, throwing in circumstance modifiers if the stats are near to equal, and then narrating the results, it's imperative that your GM be imaginative, flexible, and completely unbiased. A good GM can run a great game simply by minimizing the system, and having been to two Ambercon Norths (dedicated Amber gaming cons) I've played with some good GMs. I've also experienced bad Amber GMs, but they don't last long.
The system, because it's so simple (4 stats and a handful of powers, plus optional items) is easily converted to any rules-light setting. I've personally played a one-shot Highlander variant (the Warfare auction was fierce) and I believe that others are quite possible.
Basically, Amber is a game that imposes the minimum system necessary to rank superpowerful beings, and has no resolution mechanic other than "Okay, who's got a higher number? They win."
It also makes a great LARP system. Combat came down to a GM looking at the character sheets, saying "You fight. He wins, by a small margin, but is injured a little. Now act it out." or some such. It made for a very immersive experience.
Of course, true Amber fans will realize what I mean when I explain that I was playing an unknown character, and beat Benedict in a fair fight. That somewhat colored my perceptions of the game.
In conclusion, I like the game for some things, although I haven't played in years, and my wife is a huge fan, and still plays online.
--Seule