It's okay. I think it could have been named better.
I understand their reasoning for not having a downside as part of the main mechanic, but at the least I would have expected more cards to add a downside. Like some powerful mythic with a really strong effect whenever the Ring tempts you, but when it temps you for the Xth time you lose the game, something like that.
The mechanic is very nice flavor-wise and fine as a mechanic but it doesn't scratch any of my MTG itches. I'm a fan of combos and engines, and the mechanic does not lend itself well to that play style.
I think the way it works is fine I just wish that when you were tempted you didn't have to pick a different creature every time to become a ringbearer, moving the ring around is kind of a pain. You should be able to pay mana or pay 1-2 life to keep that creature as your ring bearer.
Oh, I just re-read it. That kinda sucks...even more of a flavor fail than I thought. I saw it as the ring tempting other creatures and them fighting over it. Dang that's just, here's a good aura essentially.
I don't like it. I find it hard to remember which abilities are granted to the ringbearer.
It didn't have much on an impact on the games I played at the prerelease.
While I somewhat get the idea that the bearer being a removal magnet is the "downside", I don't think they really got there with the flavor of the mechanic much at all. Creatures die in the game - that's just what happens. It's not really anything special for a mechanic that's supposed to be themed around something like this. It really would've been better served (again, flavor-wise) having more swingy highs and lows.