User interface is clean and easy to use, probably one of the best I know. DNS management is easy to use even for non technical users. Their reselling system works, and give you a business opportunity. They give you a broad number of services, and discounts based on volume, for a reseller it's a good choice as your clients won't have the same prices as you.

The price that Gandi offers on the more unique domain extensions have been among the most reasonable that I've found, and they periodically have really good promotions.

If there's one truly fabulous thing I can say about Gandi, it's that I have had absolutely zero issues with the actual stability and performance of the service since I switched my domains to it several years ago. I've never once worried about an error or an outage. Everything works exactly like it should. It's nice to use a domain registrar that doesn't try to shove extras and add-ons down your throat, and doesn't try to use sleazy marketing techniques to get business.