Originally my ranting response to why Jean/The Phoenix's death in "The Phoenix Saga" and why superheroes in general can be supremely boring to read about:

One of the main problems with comic stories is that heroism and epic sacrifice are often intertwined with death (i.e. the supreme sacrifice) and/or risk. Without either of those two elements, heroism becomes flaccid and there is no real sacrifice or epic quality to the "heroes". It becomes a tale told by an idiot, full of sound and fury, Signifying nothing (from Shakespeare's "MacBeth"). This was actually discussed in Greek myths - the gods and goddesses were said by some to only be heroic during the chaos of primeval age when they needed to tame monsters and natural forces. After this was done, and they attained immortality and omniscient powers, they no longer had any risk associated with their great deeds. After humans appeared with their "curse" of mortality, the ideal of heroes became identified with the fact that when they died, they could get rewarded in the Afterlife or exalted by other people. It was their lack of omniscient powers and their fragility that allowed them to be heroes.

Major comic book superheroes fall into the same category. They are all essentially gods. Death is no impediment, their attributes and traits are so far above the average human that even their heroic actions start to seem humdrum since its' not a difficulty for them, despite how much red ink is used to color a page, and ultimately they risk nothing.

Jean Grey's death occurred during a pivotal moment in Marvel's history. If you research the backstory of the creative vision and editorial mandate, a surprising fact emerges: Claremont and Byrne really believed that eventually, the X-Men's mainstays could and would retire to move on with their lives and some of them might not survive unscathed. There were numerous versions of the Dark Phoenix story: 1) One of which had Jean suffer a psychic lobotomy at the hands of the Shi'Ar leaving her without her powers and with the mind/feelings of an adolescent.

2) Another version had the events play out in the way they generally did, but Cyclops would leave the X-Men and after meeting Madelyne Pryor, would not come back except for the occasional mission (basically how Havok and Polaris were initially treated).

3) Still another version had the Saga have more to do with Jean undergoing the first secondary mutation, have her powers amplified and deal with having access to such a high power level in much the same way a drug addict had to deal with their highs and withdrawals. Ironically, there was an element of sexism in how Jean was treated, in that there are many high level male beings in Marvel, some of whom are human, who never seemed to have much problem containing their power, whereas she (and other high level superheroines) suffered mental instability or infertility. In fact, the reason she fought and beat Firelord was because she initially was supposed to do the same to Thor to prove her new power level but the editorial team didn't want his masculinity invalidated by being defeated by a heroine, so they used a character that had been referred to as being close to Thor in power as a stand-in.

Byrne and Claremont (and many of the other senior creators at the time) legitimately wanted the characters in the Marvel Universe, especially the X-Men universe, to be mortal and not be treated as untouchable icons the way the DC Big Three often were.

The return of Jean Grey from the bottom of Hudson Bay invalidated many high points from The Dark Phoenix saga but at its' core, it was a way to resuscitate the character, bring her back for X-Factor (the creative lead for that never wanted her to die in the first place) and at least say that because the cosmic being copied her intrinsic nobility, Jean deserved some of the acclaim for its' sacrifice. But the problems came into play when Marvel's heroes started to be elevated to an immortal status. If Jean came back, but repeated the same story as the Phoenix Saga in some form over and over again, this not only invalidates the initial sacrifice when the cosmic entity killed its own mortal form but also neutralizes any forward development for her character. Jean Grey as a character had years of development w/o the PF and as a character in her own right, but Marvel wants to tap into the nostalgia of the DP Saga and creators want to do their own take on the Phoenix Saga. The result is a lot of repetitive, cliched storytelling, redundant story arcs and a general malaise in regards to the Phoenix in the Marvel Universe as a whole.

There is no drama in knowing your "superhero" is not going to die, is engaging in "risky" activities with no possibility of death/injury and that the same storyline will be recycled in five or six years.

At the end of the day, the death of superheroes is boring because it means nothing. I'm not sure there is much of interest to talk about, because the act of death doesn't remain permanent for them, choosing death (via suicide, choosing a fate worse than death ((see: Cyclops becoming merged with Apocalypse)), or fighting an adversary beyond their means) carries no weight and since they come back anyway, there is no epic quality to anything they did.