It's easy to use with no unnecessary options or features that you don't need! The only thing I dislike about lightning js was how slow it took compared to other frameworks like AngularJS etc., but now there are new updates coming out which will make things faster again in future releases so not much of an issue anymore :).
If your looking into using this framework then go ahead because its very simple yet powerful at same time. There isn't anything really bad i can say either as everything works fine when used correctly (which would be if u know what ur doing).