Loved the series, the one part of the series that I did truly dislike was at the very end when it's revealed that Sam never gets to go home. It made me very sad.
Not every show needs to end on a happy note. Real Life doesn't wok that way so why do we expect it from shows.
Because TV shows aren't real life and shouldn't reflect that. Especially sci-fi and fantasy shows. After all, what happened to "suspension of disbelief"?