Way back in 1989 when I started gaming, I started a quest without even knowing it.
Shortly after my first few dungeon crawls, the quest started. I didn't know it at the time, and only recently have I even really become conscious of it. My quest was to find the greatest RPG ever.
After Dungeons and Dragons, I played scifi games like Shadowrun and Mechwarrior, looking for better settings and smoother mechanics. I have amassed a great many games, as elsewhere on my site will show you. Most of these, I'll never get to play.
Sometime later, I found Amber Diceless. I'd read Zelazny's Amber and loved it, at least the first five books. The diceless approach was good, because Amberites were ridiculously powerful compared to almost everybody and everything else. The downfall is that the game was nearly systemless. Even adding the house rule about description affecting the outcome wasn't enough to make it a really great game. In the end, it was only a really good game.
Then, I found Talislanta, specifically the fourth edition, with John Harper's excellent system. One single die mechanic governs everything, and magic is your own creation entirely. I dearly love Talislanta for the creativity that it engenders in the magic system, and the absolutely huge rich setting.
Recently, I found Nobilis. This is my current favorite, and I'll tell you why. It's diceless, but not systemless. Your character can do miracles, but not without limits. Run out of miracle points, and you're down to your base abilities only. The game focuses on the players creating the story, much more so than most games I've seen. The players create their characters, their home and their god they serve. Like Amber, each character is blessed with immense power, but unlike Amber, they also have great responsibility: Protecting some aspect of reality from destruction.
Nobilis focuses on character, or at least the GM should make sure that the game does. When one can do such miracles as lifting mountains on a whim and raising a temple with little more than a thought, physical conflict becomes... blase.
And this is what sets Nobilis apart, at least in my mind. Nobilis isn't for everyone. Most RPGers are just looking for another slog through a dungeon or abandoned space station to get more XP for kewl powerz; In Nobilis, you are a god, and you get to figure out what gods do all day.
The book itself is a monster, 11 inches by 11 inches, and almost 300 pages. Most of the book is devoted to how to run a game. A GM of practically any game would be much better off by reading those chapters.
In regards to my quest, Nobilis isn't the perfect game, it's not the end-all-be-all game. But it's a game distilled into what I love best: character driven stories. Dungeon sloggers look elsewhere.