5e will probably be remembered as "Everyone's* Second Favorite D&D," if it has a positive legacy over time. I've seen lots of people laud it as, more or less, the "inoffensive compromise D&D," the D&D that a group with widely diverse, specific tastes can agree to play without (too) much grumbling. Because that, more or less, is the One Unique Thing 5e brings to the table; it doesn't really try to do anything "new," instead being Just Enough Like whatever any given person* looks for. In not trying to be distinct, it may manage to be familiar enough over the long haul.
But, as with anything, this can be flipped around if people become more critical of it over time. Like I said before, 5e intentionally wasn't trying to bring New Stuff into D&D--and for some people, that's not "Doing Old Stuff Right," it's a lack of innovation. Instead of being remembered as a point of unity, it may be remembered as a point of blandness. Instead of being remembered as the great alt-game when you can't get your first choice, it might be seen as the game that doesn't achieve any particular goal better than an easily-acquired alternative (e.g. if you want deep character options, PF is way better; if you like ultra-simple fast play, retroclones do it better; if you want a more narrative-heavy game, D&D has never been your best option; if you want minimal DM overhead, 4e or 13A is better; etc.)
For now, it's certainly getting a positive reception. But "early" responses, even in the sense of "a couple years in," don't always reflect the lasting perception. It took a long time for the current perception of 3.x to coalesce. And just as support can wane before waxing bright again, as the OSR movement showed, so too can interest wax substantially before waning with time. There may also be other reasons to question 5e, much later down the line; for example, DM's Guild is often cited as WotC's solution for how to provide content without creating content themselves. Going the way of the OGL glut (reams upon reams of chaff and relatively little wheat to show for it) is one potential problem, but there's another that most people don't seem to consider much: DM's Guild is a service provided by the company. If the game actually does end up depending on it in order to meet 5e fans' needs, and then the service later gets pulled (as all services eventually do), 5e may end up in a worse position than 4e did. At least the 4e OCB was merely (very) useful, rather than fulfilling a need.
*Where "everyone" and "any given person" excludes most 4e fans, of course. I doubt I need to explain why.
