Season three of the definitive edition contains the 37 episodes, and also the following bonus material on DVD five:
1. The famous writer's school promo
2. SciFi Channel Twilight Zone marathon promo
3. Rod Serling's Night Gallery promo spots
4. Season 3 billboards
5. Season 4 photo gallery
6. The Twilight Zone comic book in .pdf format (which seasons 1 and 2 have and presumably 4 contain also--I haven't viewed season 4 yet)
There are also commercials for Colgate, Wildroot Cream Oil, and Oasis menthol cigarets
The Night Gallery promo spots include:
5. Station IDs
In addition to the above bonus material, the DVD also contains the following 4 episodes:
1. The Dummy
2. I Sing the Body Electric
3. Cavender is Coming
4. The Changing of the Guard
This DVD has a little more bonus material than the bonus DVD for season 2, which has five episodes. Season 1 has the most bonus material, since it consists of 6 DVDs with the last one all bonus material. Seasons 1 and 2 are both five DVD sets (and probably season 4 too, I just haven't looked at it yet).
I also noted that the season 3 episode introductions differ slightly from seasons one and two. The woman's eye image has disappeared (which didn't appear in the first season), and now there is a receding spiral pattern. In the second season, Serling's voice introduction is worded differently, which seems to be preserved in the third season. Also, the Twlight Zone title explodes or shatters noiselessly at the end into little fragments before fading away now.
Also, a brief note on the filming locations, which included the 4th Street Viaduct, Los Angeles, California; the backlot, Universal Studios, Universal City, California; Golden Canyon, Death Valley National Park, California; Lone Pine, California; Metro-Goldwyn-Mayer Studios, 10202 W. Washington Blvd., Culver City, California; Zabriskie Point, Death Valley National Park, California.
I note that Death Valley was also used as a location for the episode in season 1 in which the three astronauts appear to be marooned on a desert planet (unfortunately I don't recall the name), but it turns out they are just outside Las Vegas.
As others have already commented on the individual episodes, I just wanted to make a few comments on the series as a whole and perhaps how it was influenced by the cultural milieu of the time.
It was the drab 50s and then turbulent 60s, and the Cold War, with its threat of possible nuclear annihilation, was in full swing. Perhaps that explains the pervasive film noir ambience and dark mood that often hangs like a pall over many of the episodes. Although the characters are drawn from all levels of society and from all walks of life--from two-bit criminals to the rich and famous--many are just various and sundry low-lifes, riff-raff, criminals, and grifters. And then there are the simply down and out--the bored or emotionally overwrought, middle-aged and overstressed, desperate housewives, the dyspeptic, dispossessed, or depressed, and your average guy just down on his luck.
Almost every human emotion or character flaw or neurosis is explored: loneliness, depression, euphoria, greed, obsession, gambling addiction, hypochrondria, the lust for power, the fear of death, feelings of inferiority, failure, and inadequacy, feelings of ugliness and beauty, the stress of modern life, the old and unwanted, the young and neglected, the dispirited but still hopeful, the dispirited who have abandoned all hope, the highly successful who find their success and fame empty and meaningless, the losers who find their failures just as galling and damning, the boredom of a comfortable marriage and respectable middle-class existence, the boredom of the single and lovelorn, the desire to live forever, and on and on. Modern civilization and its discontents (or more like 20th-century America and its malcontents) seem to march by in all their false and meretricious glory. If this was the dull and malaise-ridden 50s and early 60s, one can only wonder what Serling would make of our frenetic and divided and paranoid post-9/11 world.
One funny aspect of the episodes is how unflatteringly writers themselves are portrayed. The episodes starring Keenan Wynn (in the first season) as a America's most famous (but philandering) playwright and Richard Haydn in the second season as a snobbish, effete, arrogant, spiteful, and verbally abusive wine and food writer with a short temper and a sharp wit and tongue, don't exactly portray writers in a positive light. :-)
In fact, overall, the series is notable for how many unsympathetic, unprepossessing, and even despicable characaters where often in the lead roles. :-)
So all in all, a truly unique piece of Americana from a long lost era whose themes and stories have held up better than I expected.