At first a lot of things i.e. their range of services (like share, social login, ratings etc.), but afterword, as we went through configuration and implementation, I started disliking many of these things
It is difficult to configure things. The gigya console does a terrible job in giving you options, at least when I used it a long time ago.
Ratings: Out of the box doesn't allow you to change layout, or enable/disable features like commenting.
Share: I received terrible customer service around enabling simple share options for our site. It is difficult to customize it for your look and feel, their share code isn't optimized for the web.
Support: I find it bad. All they do is send you links to documents. They don't take the time to understand your site structure, instead they try to understand the issue only from a high level (support should get into the weeds of the issue), and send you links that contain lines and lines of code and functions and methods.
Their effort estimates are extremely high i.e. if you are working on a custom functionality with their support, and have to pay for the hours, their hour estimates (how long would it take to do something) are really high.
their Analytics isn't that great either ... gives you the high level/popular analytics but cannot go into details as in "who shared what article where", "which article was shared where and how many times"