Starting in 2004, DC Comics has been suffering from an over-abundance of angst, psychosis, violence, gore, rape, and murder, all for shock value.
There used to be a motto about death in comics: "Only Bucky stays dead."
Bucky was the WWII sidekick of Captain America who died in battle.
Whenever a character would die, it would be a waiting game before they were brought back to life.
DC's Silver Age was a re-imagining of the Golden Age. Characters like Green Lantern, the Atom, and the Flash were given different identities, designs, and sometimes abilities. Later on, it was determined that these were "legacy" characters. Al Pratt was the Atom for a while, then it became Ray Palmer's turn.
Then, in 1985/6, during DC's Crisis on Infinite Earths, Barry Allen, the Silver Age Flash, was killed. Not much longer after that, Jason Todd, the second Robin was killed. They served as a postscript to the Bucky motto.
Barry was replaced by his nephew Wally West, the Kid Flash. Jason was replaced by Tim Drake.
In 1971, DC introduced John Stewart as a Green Lantern. It's the first time a black man wore a costume traditionally worn by a white man. However, Stewart was not a replacement for Hal Jordan; they were members of a galaxy-wide police force 3600-strong.
In 1994, DC published a storyline called Emerald Twilight, continuing from a "Return of Superman (from the dead)" story. Green Lantern Hal Jordan goes insane and destroys the Green Lantern Corps. One GL ring is left, and given to Kyle Rayner (initially of Irish decent, later to be revealed as Irish-Hispanic) to be the sole Green Lantern. Soon after in the Zero Hour miniseries, Jordan tries to remake reality, and is defeated. In 1996, in an attempt to redeem himself, Hal dies by restarting the Sun in Final Night. Kyle would later re-create the Green Lantern Corps that John Stewart would join again. Somewhere during this era, Stewart was recruited to the Darkstars (don't ask) and crippled in battle, and healed by Jordan just before or during Final Night.
Why the GL ring never went to John Stewart is beyond my understanding. At the time, interest in the GL "brand" was waning, and a complete reboot was the editorial decree. Something similar was happening with another green-clad hero.
The reaction that Hal's death garnered was mixed. A lot of fans were outraged.
Also in 1994, DC introduced Connor Hawke, the Black-Asian son of Oliver Queen, Green Arrow. Connor shared his father's past time and masked identity, working together and separately. In 1995, Queen dies in an explosion, leaving Connor as the sole Green Arrow.
Wally West, Kyle Rayner, and Connor Hawke form a similar friendship that their forebearers did. They worked together in and out of the Justice League.
In 1999, Cassandra Cain (Asian), was introduced as Batgirl during the year-long No Man's Land story. She was brainwashed, took over a group of assassins, went on a killing spree, and kicked into editorial limbo.
In the early 90s, Stephanie Brown was introduced as The Spoiler. Teen daughter of a third-rate Batman villain, she served as a foil for her father, as well as Batman and Robin. She tried to gain Batman's acceptance. For a time, she did. She was Robin for all of three months, and was fired. She then started a gang war, and was viciously beaten. Her death was faked, and then brought back to Gotham. She then became Batgirl after Cassandra's...complications.
In 2004, Ray Palmer, the Atom, was driven mad by grief due to the events of Identity Crisis and disappeared. A student of his, Ryan Choi, took up the mantle.
Jason Todd, Oliver Queen, Hal Jordan, and more recently Barry Allen have been resurrected. (Bucky was also revived, but that's a different universe.) Ray Palmer is also back in action, but he's not at the top of his game.
Connor Hawke was shot by a poisoned bullet, comatose, revived, brainwashed, DNA spliced, and eventually revived again. He's still a little scatter-brained, but he remains a competent martial artist.
Kyle Rayner (the "savior" of the corps), along with John Stewart and others, were sidelined to a degree by becoming Alpha Lanterns, a sort of Honor Guard of the GL Corps. All to keep Hal Jordan in the spotlight.
Wally West got similar treatment; he's still a Flash, but Barry is THE Flash. His costume was tweaked to line up more with the animated version.
Ryan Choi was killed couple of weeks ago, to show how bad-ass a group of assassins are. Ray Palmer is now THE Atom again.
While I disagree with killing off the old to make way for the new, I disagree even more with killing off the new to make way for the old just to feed one writer's Nostalgia Fetish.