People look at me like I'm crazy when I tell them I've been to just about every major national park in the lower 48, and that my favorite is Death Valley. This is why. I always visit in winter - usually between Feb 20 and Mar 10 - when the wildflowers are in bloom and the temps are just perfect. Daytime highs in the 70s (maybe 85 at Badwater), cool nights in the 40s, clearest, most brilliant night-time sky you will ever see. Oh yeah - and no damn bears!
If you think this place is hell on earth (and it is 8 months a year), you really need to see it's other face - millions of purple and yellow wildflowers popping out of the hottest, driest valley on the planet, towered over by the snowy Panamints! You can stand in Lone Pine and look off to Whitney in the distance with a vertical relief of about 10,800 feet, and be mesmerized. It's better in DV: you can stand on the valley floor at Badwater and look up at Telescope Peak right above you with over 11,300 feet of relief. Something like the 3rd highest relief or apparent elevation in the world after Denali and Rainier, but don't quote me.
It's amazing the number of Californians that I've spoken with over the years that have never visited this place during the best time of the year. It's right in your backyard folks, and it's worth a few hours on the road - especially since the Sierras are not easily accessible Nov-Mar! In fact, I'll be there again this year (March 2-8), during prime wildflower season. This will be my 7th trip in the past 11 years coming from the other side of the country for no purpose other than to camp and hike in DV in the winter. It is so worth it!