A lot of people hate on Prequels in concept because "We know what's gonna happen", ya know what, that's what I like. they are denied the option of doing the most shocking thing possible just because it's shocking.
A lot of films have great surprises/twists to them, and they're very good, but that's not the be-all/end-all of film making. There are a lot of people out there who feel being "predictable" is the worst criticism a story can have leveled against it, and to me that is a stupid way of thinking. Too many mysteries are ruined because they cared more about the reveal being unpredictable then about it making sense.
Knowing what's going to happen doesn't hurt historical films, or faithful novel adaptations, there is no reason why a fictional prequel which often has more innate wiggle room then those should be a problem.
Being predictable does not have to hurt your story. Let's take unmAsked, the second season finale of Pretty Little Liars for an example. Lots of people complained at the time, because there are always some complainers, that Mona being -A was to predictable, even those who hadn't read the books had heard Mona was the first -A in them.
I predicted it would be Mona, and all through that sequence of Spencer and her in the lair I knew what was coming. But the actual reveal still had a huge impact on me, My heart was racing, it was tense as hell. Because being predictable doesn't mean a damn thing if it's well dome.
I have grown to love PLL even more since then, I consider it the Greatest show in the history of Television. I loved the latest 5th Season finale, but I still feel cheated that they changed the nature of the Twin issue just because everyone was expecting it. It'd have been much better if they'd simply followed unmAsked's lead. I'll keep watching PLL till the end, but the more I've digested Dollhouse the more I've come to consider it the most disappointing season finale.
So I think there is a great virtue in knowing where the story is going, with the question merely being how. So let's return to the subject of actual Prequels. I liked watching the Star Wars Prequels knowing they didn't have the option of randomly killing Obi-Won or Anakin, or Yoda or the Droids or Chewie or even Organa just so it'll be unexpected. Really my only criticism of ROTS is that Padme dying does create continuity issues with what Leia told Luke. But it wasn't to be shocking Lucas did it, he wrote himself into a corner with the theme of Anakin's weakness being not handling loss, for that reason I can forgive it.
If The Force Awakens kills off OT survivors (besides the Droids) that wouldn't be shocking, that would fit the pattern of how the SW legend has worked so far, Luke is now in the role of Qui-Gon in Episode I and Obi-Won in Episode IV. But if one of the 3 new leads is killed off, that would be a cheap ploy, (Also the Droids shouldn't be killed off because they should be the ones who see the whole story, I went off on that already).
I am not familiar enough with Abrams to guess how likely he is to pull a ploy like that. But with the Prequels I didn't have to worry.
That of course does lead us to the issue of Quasi-Prequels, like Gotham on Fox. It's a Prequel in format, major Batman characters before they become who they'll become, though a few pretty much are there already. But it's not in continuity with any specific future Batman adventures we've seen, the Batman mythos are subject to change, and that's good I want different takes to be different, but, certain things should be unshakable.
A recent statement from the producers of the show said that "Not everyone from Batman canon will survive the series". They want the option to kill off characters that viewers are assuming are safe because they appear in Batman comics and movies.
I fear what this means for the end of Season 1 with their generic serial killer who kills women because of his mommy issues story-line is probably that they're gonna Fridge either Barbara or Leslie Tompkins. Either of those options will tick me off for no other reason then my annoyance with Fridgeing in general.
In terms of how that breaks with Canon, Tompkins is like the character she's named for in name only, and is a character I never liked really anyway (even before War Games and War Crimes). But if they kill off the mother of one of the DCU's most important and iconic characters before she has that child, I will be pissed and will likely quit the show simply for that. And that is independent of my personal wish of wanting Barbara to become Batwoman.
Smallville was in a similar place to Gotham, during their good years they never did anything like that.
But in Season 8 when they killed Jimmy Olsen only to then reveal that was never really Jimmy Olsen. I was pissed, and was unable to keep consistently following the show, I checked every now and then, and saw how it ended, which I had very mixed feelings about.
This comes back to my issues with how TV shows are made now days in general. Anything with a Genre element to it they feel they need to kill off at least one Main or significant Recurring character every season to to keep a sense of danger. The Vampire Diaries which I loved watching for awhile, was from very early on one of the worst offenders of this, they killed someone off every few weeks.
Gotham is about the Batman universe, one defined by it's darkness and Pulp/Film Noir roots. So you may feel "certainly a Batman show ought to be killing people". But Gotham has done a great job of showing this is a violent and dangerous world without needing to kill any major characters. We see Penguin and other villains killing people constantly. We don't need to butcher canon in order to keep a sense of danger, and dying isn't the only bad thing that can happen to a character.
Deaths should happen, but they have no impact if they happen all the time, like on Game of Thrones or True Blood.
Buffy The Vampire Slayer never killed off an important character until 3 quarters of the way through Season 2. That did have an impact. And then they didn't kill off anyone in Season 3, or 4, there wasn't another death till 5. During the last season and a half the deaths increased to help show how things had escalated.
That's how Gotham should be, we're not in the world of Batman yet, there is nothing to escalate to if already the lead's love interests are being killed off for season ending shockers.