While it is a good read, there is a lot of violence and some implied sexual content.
With the death of a good friend, Eragon must face life, and his training in Du Wendel Warden, without any companions. While Galbatorix attempts to expand his power in Alegaesia, Eragon grows rather fond of a certain Elf and also finds that he is not the only Dragon Rider left.
This book has very loose morality; Paolini seems to be very open minded.
In Eldest especially, there is a good bit of questionable content. Getting pregnant before you are married seems to be acceptable, even though tradition frowns upon it, and it is alright to live with someone and not be married.
There is no mention of church or the Bible. There are, however, several mentions of gods. The Dwarfs have theirs, the tribes have theirs, and the Elves are atheistic. Animals (especially dragons) have souls. One of the characters is possessed by dark spirits. Eragon continues to be able to control things by speaking commands in the Ancient Language, which comes across as a kind of magic.
Many of the main characters die; Eragon is present at many of these deaths and, as we read from his point of view, it can get detailed and graphic.
Drug and Alcohol Content
Characters, including Eragon, drink wine. They do not do so often, but every once in a while it will give a reference to wine, beer, or mead. Drunkenness is not frowned upon.
Roran, being engaged, is sleeping with his intended. While it is not detailed, only implied, it is still there.
Crude or Profane Language or Content
Eragon and his cousin, Roran, both curse. There is, however, no explicit use. Paolini uses phrases such as, "Roran cursed quietly under his breath."
There is also a woman who acts like a mother to Roran and Eragon and she doesn't mince words with them; she often says some crude things.
There is no explicitly profane behavior. It is implied, but it does not go into detail.
Eldest is a good book in terms of writing and plot. You grow with Eragon through it. Paolini's writing style gets more involved as the books go on, and it is very easy to get sucked in. However, if you are to read these, I would suggest that you be on your guard; it is not best suited for children under its targeted range. Do not accept everything in these books as good.