The Store is picking up exactly what is in the specified tags in the feed:
I don't know whether that's the text you were hoping to see. Your feed has a large amount of formatted text in the 'description' tags, but iTunes does not read this tag.
This page illustrates what tags appear where in the Store and when subscribing:
(It's for the previous version of iTunes but the differences are slight, just a matter of layout.)
Note however that the image referenced in the feed does not appear when subscribing - the image has to be actually embedded in the media file. Please see this page for details: