
I like that it is easy to connect leaflet to web page. It allows to use third party map tiles like mapbox tiles. It allows to customize map, add some additional settings for final user, like markers with popups where each popup can exist any text and even fields which user can edit. Markers can be grouped to clusters and when final user zoom in a map, clusters are divided to smaller clusters and finally to separate markers. It is possible to customize markers, make their look unique. Use different third party extensions and so on. I think it is the best JS library for working with maps. It uses openstreetmaps, so it does not cost anything for developers. Review collected by and hosted on G2.com.
If your map has a lot of data, e.g. thousands of markers in clusters, Leaflet will use a lot of RAM what will make your browser freezing. It does not have as much tile designs as google maps for example. It is also built on opestreetmaps which are not so accurate as google maps API. Review collected by and hosted on G2.com.