Echoing what everyone has said. Probably the best place to buy used games. Everything is in great condition and it has always included all inserts (including DLC codes) when I have used them.
Probably the best place to buy new games too. Not directly, but through their keep it feature. Sure the game is not technically new (unless you get a just released game and you are the first to receive it), but like new games you receive all the new stuff you don't get with a used copy. For example, any DLC or codes inside the case are preserved.
The perks of Keeping are the following:
1. You KNOW it works.
2. You get all the DLC and codes from the case (they are shipped to you)
3. Free shipping
4. A reduced price (at least $5-10 or so).
The only times you cannot "keep" a game are when it is a certain age or rarity.
I would regularly keep games I received. I got a reduced price and I cannot tell or remember that they were not bought new.