Old school gaming puts emphasis on events over story, strives for slow-paced dungeon delving and wilderness adventuring, demands player skill and common sense over character abilities, and presents combat as a deadly and not-so-rewarding affair. Character death rate is considerably high, given the multitude of dangers that can insta-kill one, but character generation can be quick and easy.Having said that, there doesn't seem to exist a clear line between old school and modern in D&D. Sure, the '70s can be easily labelled as old school gaming and modern gaming features prominently since the '00s, but the time in-between appears to bring different styles and experiences to most gamers. The age running through the '80s and '90s is filled with experimentation, shifts in tone and theme, and blends different styles to create an amalgam that caters to a variety of players*. While the changes of old school gaming can be traced throughout the '80s, adventures that focused on story and rulebooks that codified rulings and house rules, I believe that AD&D2e's publication in 1989 cemented the co-existence of both old and new style. It is the time we see the term module and adventure used interchangeably; the emergence of a strong narrative in adventures, exemplified by excessive, sometimes, boxed texts; and the appearance of new ways to reward characters, for reaching goals and successfully overcoming encounters without resorting to violence, with the introduction of Story XP. These features ran along typical dungeon crawls (albeit with a narrative twist), random encounter tables, and deadly battles. Even the Gold-as-XP rule, while optional, was there (DMG Revised, pg. 69).
Modern gaming assumes that story takes precedence over events, is characterised by fast-paced action scenes with a variety of backdrops (above or under ground), requires a die roll for most actions, and embraces combat as the cornerstone of D&D, with corresponding rewards. Character death rate is significantly low, despite the endless trials and tribulations, and character creation takes some effort to be completed.
|Sample from the adventure Tower, Temple, Tomb (1994),|
featuring dungeon delving and rich backstory shown in long texts.
|Dragon Mountain (1993) and Dark Sun (1991), glorious boxed sets.|
*Also, you might want to check out this brilliant work from James Maliszewski (of Grognardia blogspot) on the Ages of D&D; he tackles TSR years specifically, as he doesn't comment on post-2000 editions.