It's an elegant mechanic when used in the right places and-or with other things and very inelegant when used in the wrong places and-or by itself, as instead of any form of granularity you've only got three options: advantage, neutral, or disadvantage.
If you're looking to impose just a slight bonus or penalty to a roll, adv-dis is overkill. If you're looking to impose a major bonus or penalty, adv-dis doesn't go far enough. And if you're not using bounded accuracy and want a system where rolls can get over 20 or under 1, adv-dis just can't do it.
Conclusion: fair to good. Not perfect, nor even close.