(I'm not against tributes/continuations/adaptations of something like BTTF, I *loved* the Adventure Games and the animated series, but something that basically reworks the franchise into something modern and does that 'Year Zero' type stuff would be a step too far for me. I kind of feel like that about Indiana Jones, even though weirdly I'm 100% okay with something like Doctor Who or Star Trek being given the reboot treatment...)
Yeah, it depends on how it's done. As with everything else, it's not the category that determines worth, it's the specific case. I'm fine with some reboots, and I think a full-on Star Trek reboot that made a clean break would've been a better idea than the sort of hybrid-alternate-reality thing they've done (if only because the use of time travel has made a lot of fans expect the timeline to be "reset," which is the opposite of what was intended), but there are cases where it doesn't seem like a good idea because of the specific route they're taking. For instance, the Ghostbusters reboot they're doing strikes me as a bad idea because they're making it just another cliched secret government program, when part of what made the original work so well was the public nature of the Ghostbusters, the way they were a business that advertised on TV and got in trouble with city officials and so on. Also because the premise of the Ghostbusters inherently allows for an in-universe continuation by having the original team build the business into a franchise, and I would've liked to see that. This reboot seems to be replacing something fresh and expansive with something cliched and self-limiting, and I don't see that as a change for the better.
But Indiana Jones is a case where I just don't see what the purpose of a reboot would be. A reboot is worth doing if it changes the original in a creative way that adds something worthwhile or brings a fresh approach. But Indiana Jones isn't about novelty, it's about affectionate homage to the cinema of a past era. What could they change that's significant enough to make the change worth doing? If it's going to be the same kind of classic adventure story set in the pre-WWII era, there's no reason that I can see to alter the continuity rather than just telling more stories in it.