They're alright. Speaking as somebody who read every single thing Card wrote up until about the turn of the century (literally everything, like down to the unpublished one-act LDS plays he wrote in college), it just doesn't get any better than Game. Its sequel Speaker for the Dead is pretty boring and not immediately relevant to the story, Xenocide is interesting but about 2 times as long as it needs to be, Children of the Mind was all over the map, and the later 'Shadow' sequels are in my opinion nothing more than a blatant cash grab. Ender's Shadow is just an Ender's Game rewrite. If you do intend to read Shadow, though, I would say read all the books in the order they were written. Don't skip from Game to Shadow.

Make sure your read Ender's Game FIRST and Ender's Shadow SECOND... let me know what you think!