If you know nothing about Halo, it's not bad. If you're a fan of Halo I would strongly caution you about watching it. SPOILERS AHEAD!
The action sequences were okay. There were a couple scenes where the movements were a bit scuffed, as if they were trying to make the Spartans move like machines. The first person fight sequences were unnecessary and took away from the action, not add to it.
The Spartans were abducted as children so they would have memories of their parents. Of course they spent the rest of their life in military facilities so a lot of it would have been repressed or forgotten.
Spartans are loyal to other Spartans first, then the UNSC and then the rest of humanity. Master Chief would not have gone rogue for some random person he just met. The Spartans were raised to obey orders and as cold as it sounds he would have killed that girl. Especially since she was a separatist.
When the Prophets discovered that humanity was the true inheritors of the Mantle of Responisibility and therefore all of the Forerunner technology, they started a genocide and eliminated anyone who knew the truth. There is no way they would have been harboring a human.