1) There's a reason the campgrounds in the park are closed from mid April to October: it's HOT.
2) It will be ~85F from the time the sun goes down around 8pm to when it comes up at 6:30am. Then the temperature will quickly go back up to 100F. Plan accordingly.
3) If you try to drive off road, you will get a flat tire, and it will take 2hr+ before a tow truck shows up. Then they'll charge you a ton of money. Not from personal experience, but we saw this firsthand a couple times in just a few short days.
All that aside, we had a great time in Death Valley. We got there right after the typical "season" ends, and we wouldn't go any later in the year. It was ~100F on both days while we were there, but in the peak of summer it regularly gets to 120F during the day and only goes down to 100F at night. We found the midday temp was just on the edge of bearable, and ice cream from the little general store near the visitor center certainly helped.
We spent about 1.5 full days exploring the major sights to see in the Valley. We camped in the aptly named Furnace Creek Campground, and we were lucky enough to get a site in the shade. On our first day in the park, we drove north to see Scotty's Castle, a mansion built around the turn of the century by an eccentric millionaire. We arrived a little too late to get a tour, but it since it is situated at a natural spring and higher up in the mountains, it was a nice little oasis from the heat of the valley. We also hiked around Ubehebe Crater (slowly and with lots of water), and checked out the Mesquite Sand Dunes at sunset. On the second day, we drove south for a quick and early hike in Golden Canyon, and then hit some of the major attractions like the Artist's Palette, Devil's Golf Course and Badwater Basin.
View from Zabriskie Point
View from Zabriskie Point
Artist's Palette at sunset
Lizard tracks at Mesquite Sand Dunes
Devil's Golf Course
Badwater Basin, the lowest point in North America at 282ft below sea level
Ubehebe Crater
Golden Canyon
