I was never a particularly big Star Trek fan, though I did like the feature films with the original cast and very much respected The Next Generation for continuing that legacy, and in many ways improving it and widening its scope from the original series to something that was relatively sustainable as a franchise.
I more got interested in it over recent years through fan discussions of it with people who have much more investment in the series than I had, such as the recent
Red Letter Media discussions of their top 5 TNG episodes. Plus
Pogo's Data & Picard track and its "Incredibly unbroken sentence moving from topic to topic no one had a chance to interrupt, it was quite hypnotic" is Patrick Stewart's equivalent of "supercalafragilisticexpialadocious" phrase and works as a great tribute to his character!
Similarly I really liked the first two X-Men films, and of course especially Stewart's interplay with Ian McKellen as the duelling Professor X and Magneto characters. Though as with Star Trek, and I hesitate to bring this up especially so soon after his passing, but is an important part of assessing the legacy, I think what happened to both his Captain Jean-Luc Picard and Professor X characters illustrate some of the dangers of becoming quite so iconic to a franchise, such that they cannot gracefully let go of such a lynchpin character.
It feels as if a lot of the recent versions of those characters have been obsessed with securing a legacy, or finalising their position in the universe of the franchise, but we are in an era of film and TV making where no-one is ever really done with their character until physically unable to do the role any more (and with CGI/AI maybe not even then, as we saw with the Ian Holm 'cameo' in Alien: Romulus most recently; or Peter Cushing in one of the Star Wars sequels). I sometimes think that this could be called a process of 'toxic nostalgia', because these franchises cannot stand on their own feet without having to rely on certain characters; certain actors; certain pre-existing beats of storylines to prop up any new elements that are introduced. Which is something that has been causing all of the cultural conflict in recent years that we can see expressed both by OG fans on the one side, and people wanting to revise legacies on the other. When really the best thing for everyone was to leave the past in the past and move on, and succeed or fail on those terms - because going back and 'revising' taints the pre-existing and makes the new seem hollow and piggybacking in comparison. I do not begrudge original actors being excited to return to their iconic roles, or even just leveraging their role for a big paycheck, but the problem in recent decades has been that it has become way too easy to go back and re-do, rather than move forward and explore new territory.
Patrick Stewart's characters are really interesting to view through this lens, because there have been multiple times where he brought both Captain Jean-Luc Picard and Professor X to graceful, moving endings for their character. Where of course as an audience member it is sad to think that we will never see them again, and would love to have spent more time with them, but if they had to go then this was the perfect way to bow out and exit stage left. The final "All Good Things" episode of Star Trek; The Next Generation; and particularly 2017's Logan feel key in this respect.
The only problem is, to steal a quote from The Stanley Parable's loading screen: "the end is never the end is never the end is never the end..." ad infinitum. And after those perfect (or at least apt and character appropriate) endings, the franchise has to continue somehow, and actors are lured back for further entries. Which undermines the previous departure and makes any return feel hollow. The Picard series seemed like a straining attempt to secure a legacy for a character that already was iconic and beloved, and found little to justify its existence, or really anything in particular for the elderly Patrick Stewart to do, for its first couple of seasons until the third realised that if you are just going to wallow in nostalgia, you either go all or nothing and have to reunite the whole original crew for a final voyage (which is something that the original Star Trek cast did a few times themselves in the feature films). On the same note, that is something that also makes the rumours of Ian McKellen returning to his Gandalf character at some point concerning as a similar situation (see also Robert Downey Jr 'returning' to Marvel, as a different character seemingly. Or Hugh Jackman having seemingly been desperate to have retired his Wolverine character multiple times before being brought back for another entry).
The X-Men series (and this applies to the wider Marvel Universe in general, despite X-Men having been a separate entity until recently) is kind of even worse for this, because with the Multiverse element you may not even be
getting the beloved version of Professor X that you know and love, just a whole new character who just superficially looks the same. That is kind of fundamentally undermining of character, the actor playing them
and the lore of the franchise as well, so its a very dangerous game to play unless you know what you want to do or say with using those kind of paradoxes. So (and you could apply this to who the 'real' John Connor is in the Terminator franchise as well, which also appears to have been handled on the fly rather than having any character arc through the process mapped out) who is "Professor X"? The one from the first few films? The older man from Logan? A Professor X from other timelines? And if it is not the Professor X that we know, how can the instance of that character still be expected to have the weight of legacy behind it, or command that legacy?
So it is a complicated mix of real world aspects (the actor wanting to revisit their character; the studio wanting the name of a key actor to inspire audience recognition) and fictional aspects (the weight of the character's own legacy and what that means to the audience to inspire their interest) that makes something like celebrating Patrick Stewart for his Star Trek and X-Men roles slightly more complicated in the current moment than it would have been, say, a decade or two ago.