In an era of reboots, revisitations and revivals of old franchises and settings, one is faced with the often discomfiting experience of trying to reconcile the old with the new. When the transition is smooth, it is hardly a struggle; but as, more oft than not, the two do not quite align in themes or style or narrative, or are at odds in established details versus innovation, the question is raised: where to the draw the line?
Suffice to say, given my interests, this question has arisen rather frequently of late.
Sometimes, it is easily resolved, as the new explicitly places itself as firmly outside the old canon — such as the Battlestar Galactica reboot, which kept only the broadest outlines of its predecessor — allowing it to be judged largely on its own merits.
This becomes rather difficult when the putative "reboot" keep referencing the old canon in some misjudged stab at "nostalgic fan service" drawing constant direct comparisons, especially while demonstrating a complete lack of understanding of the material being used to the point of sometimes seeming disrespectful. But the conundrum is worse still when this occurs as part of a revival that claims to be a direct extension of the old canon.
So where can one draw the line for sanity's sake? Personally, I take a cue from the established concept of "B-Canon"
For those unfamiliar, there is a long-standing graduated model of "canonicity" in established franchises, ranging from "C-Canon" at the bottom, which is typically the realm of peripheral licensed merchandising loosely tied to the material; "B-Canon", which is the position occupied of third-party adaptations of the material; and "A-Canon", the creators' vision that both establishes and supersedes all the rest.
How does this relate to the question?
Considering that, prominence and medium aside, many, if not most, of the fresh iterations are not the work of the original creators, one can logically place these in the "B-Canon" realm, irrespective of what their producers may claim or intend — i.e. one of the most current subjects of canon-clash, the new Star Wars sequels. Irrespective of whether one favors the new material or loathes it, or the relative merits of old versus new, it is undeniably being made sans the input of its creator, George Lucas, and with only the shell of "Lucasfilm" retained.
The post-Lucas Star Wars films are effectively a new "Extended Universe", presented rather in the medium of film.
This means that, even if the new films evoke the originals, extend their narratives, involve original cast members, these have more in common with the "B-Canon" of the old "Extended Universe" than that helmed (for better or worse) by Lucas himself. These are adaptations, not really part of the original canon, but parallel to it, interpretations. The degree of license taken with the material, the general reuse of established tropes and reliance on reordered narrative elements, the overt fan service — all these are remarkably consistent with Star Wars "B-Canon" of all kinds, from novels to television series to gaming, to a degree that effectively negates the claim of Disney that these represent "A-Canon" in character or content.
Of course, this sort of obvious "regurgitation versus innovation" aspect is not truly the key ingredient, but rather the simple fact that the new material is the work of a new party, rather than the originator or the same unbroken production linage of the source material.
To make a less hot-button example in a less contested medium, one would not expect that any new material for established literary setting, like, say, Sherlock Holmes or Middle-Earth, supersedes what the Arthur Conan Doyle or J.R.R.Tolkien established themselves, no matter the form, medium, or quality. The originals stand, as the creators' role is an intrinsic element of their canonicity, and the new would simply be treated as adaptation: "B-Canon" at best; disregarded as irrelevant, at worst.
Thus, I can draw a clear line between old and new — even if it does not necessarily improve my judgement of the given reboot, revisitation, or revival, which still must succeed or fail on its ability to adapt its source material effectively and employ its medium well.
Then there is the vexing matter of an original creator returning to their prior oeuvre and screwing it up — but that is a completely different kind of headache...