First of all, I cannot get it to work. Definitely a lack of instructions here. It creates a custom post type, but I don't know what to do with that. Does it use the images attached to a post/page or those attached to the custom post type?
Also, I noticed some strange things.
To start, the plugin appears as "Page Gallery Slider" instead of "jcarousel Horizonal slider" (don't mind the missing 't' in horizonTal). In the plugin description it is called "Best Gallery Slider", which also can be found back in code, where there are numerous usages of "galleryBest" and "bestgalleryslider".
Furthermore, the version information in the changelog part of the readme.txt file conflicts with the version mentioned in the plugin's main file (which is the same as mentioned here in the repo).
All together it looks like either a fork of another plugin or a collection of scripts from different sources. In both cases, there's no mentioning of the source, which thus would be a violation of the GPL. (Maybe I'm all wrong here, but this is just my perception.)