Top of the list is the Sabonis extension. Sasha sounds like a good player, but probably more of a good bench guy. I can't get excited about the other additions yet until I see more of them. The Barnes contract makes him that easy to move, and hopefully Monte will find some value for him in the future. It's a good offseason, so I give a B.
Now if you include summer league in "the offseason," then I give the offseason a B+ on the sheer weight of Murray's performance. The absolute key to the upcoming season is Murray. Fox and Sabonis are constants. Murray is the X-factor. He looked fantastic in summer league. He looked stronger, aggressive, and confident. He's got much more room to grow to reach his ceiling, imo, and if he takes a good step upward next year then the Kings take a good step upward. If he doesn't, then the Kings should still be in the playoffs, but not as scary as with a Murray who people can easily see as a future All Star.