I think Gen 2 and Gen 5 have aged the worst. Gen 2 games were developed in a time where tech constraints meant the best that could be done was emulate the arcade experience of the time. They were typically simple games focused on getting high scores. Occasionally you'd have something that broke from that formula, but even then those were also very simplistic games. The simplicity doesn't make them bad, and some of them hit a very satisfying gameplay loop, but it does mean that they lack depth. Some of them are fun to go back and revisit briefly for a casual session, but they just don't grab me like they did when I was a little kid back in the 80s.
It doesn't help that during Gen 2's heyday in the early 80s, there was a huge gap between the graphics capabilities of consoles and arcade machines (a gap that took until the mid 90s to close fully). While sprites do tend to age well, the sprites of Gen 2 games, and the Atari 2600 in particular (which was the first example of the best-selling system not being the most powerful), just don't have much appeal anymore. They're just too primitive and simplistic to hold much aesthetic value. They worked for the time, but this was the "stick figure" phase of game graphics.
With the NES, the increase in computing power allowed not only for vastly greater graphical detail, but also more sophisticated gameplay. Super Mario Bros. was truly a revolution in gaming. The diverse enemies and level design, more complex mechanics, and an definite end point instead of a simple "play against increasingly harder waves of enemies until you run out of lives" setup was something nobody ever really saw on a home console action game before then. The NES allowed for an explosion of diversity in the kinds of games that one could experience on a home console, from Super Mario to Zelda to Metroid to Mega Man to Final Fantasy to River City Ransom. And in the first half of the 90s, the 16-bit era took the 8-bit ball and ran with it, continuing to evolve the gameplay and producing even better-looking sprites, many of which still look great to this day as simple art. Games like Super Metroid, A Link to the Past, and Final Fantasy IV & VI perfected the formulas of their 8-bit predecessors. It was the Golden Age of the versus fighting game and the JRPG. The decade from 1985 to 1995 was an incredible time for gaming, and has stood the test of time.
With Gen 5, those early 3D titles came at a time when the hardware was just barely powerful enough to render polygons. Graphically, I cannot think of many games from that era that don't look like total eyesores today. In fact, even back then I thought many of them were outright ugly, the novelty of 3D models and environments not making up for their often muddy hideousness, whereas 90s-era sprites were vibrant and pleasing to look at. There are a few than aged better than others, most notably those that went for a very cartoonish aesthetic. And personally, I felt PS1 graphics in general aged much more poorly than N64 graphics. Maybe it was the more powerful hardware on the N64 combined with various bits of graphical trickery to mask the limits of what 3D game graphics were capable of at the time. But to the PS1's credit, it still managed to have a few notable games with predominantly 2D sprite-based graphics, which have of course aged far better than any 3D polygon-based visuals from the era.
And since this was the dawn of 3D graphics, that meant the dawn of 3D gameplay as well, and most developers had a hard time making games that were mechanically accomplished when the Z-axis was added to things. Stiff controls and terrible cameras were the norm in action games. For every Super Mario 64, there were a dozen others that were nearly unplayable. The genres that fared the best mechanically were the ones where graphics didn't impact gameplay much if at all (turn-based JRPGs), or were ones that tried to emulate 3D in the 2D era through graphical trickery (racing games), or were new genres that were a natural fit to 3D and where camera placement wasn't a concern (first-person shooters). Time has done most of the games from this generation no favors at all, though Nintendo and Rare still made plenty of classics, and the PS1 had a couple of games that still hold up well, maybe if not visually then at least in terms of how enjoyable they are in general.
The following generation wasn't a tremendous improvement in terms of gameplay in my experience, despite the continued advances in graphics. Emerging genres (e.g., the open-world sandbox action game) were still finding their footing, and the kinks of 3D gameplay were still being ironed out. Nintendo, after being perhaps the developer that best understood how to move gameplay into the 3D era, went through an unusual experimental phase that was frequently hit or miss. There were exceptions. Halo CE pushed FPSs in new directions, perfecting twin-stick controls and introducing or popularizing mechanics that are now genre mainstays, while Halo 2 popularized online multiplayer on consoles. Soul Calibur became the definitive 3D fighting game. Metroid Prime successfully shifted its half-namesake Metroidvania sub-genre from side-scroller to first-person action-adventure shooter. But overall there wasn't much truly remarkable about this generation to me, and there's few games from it that I actually feel like going back and playing. In fact, since I think the N64 had a stronger library than the GameCube, I'm inclined to put Gen 6 slightly behind Gen 5.
Last generation was when I felt that most studios of note really got a handle on 3D gameplay. Because it's so recent, it's hard to say how well it will hold up, but, for what it's worth, on the gameplay side there were a ton of fun games that I still play, and many titles still look pretty damn good (esp. those that got a resolution bump on the X1X). MS and Sony both expanded their efforts to produce more exclusive content, though Sony's approach was more sustainable in the long run, giving them a great assortment of in-house studios. However, Nintendo's experimental phase continued, and while the Wii had some undeniable classics, the forced motion controls may not age well in the long run.
As for current-gen, I'm not sure how it will hold up. This is still in many ways a continuation of last generation, just with prettier graphics that will age even better. The Wii U had a solid library, and I think will be remembered as a great system that went unappreciated, a victim of poor marketing and other missteps on the business side despite great games on the developer side. The Switch seems like something that will be long-remembered as well, as Nintendo is still putting out some instant classics, and in many ways is returning towards more conventional gameplay despite the unconventional hybrid hardware. Sony has put out some of their best first-party games ever with the PS4. But on the other hand, some things will not be remembered fondly.
Last generation, DLC, which rapidly became popular after its limited-scale introduction in Gen 6, allowed for games to be expanded with fresh new content to add new life into titles, but it quickly starting gaining a stigma later in the generation as many publishers abused it with season passes, online passes, on-disc content locked behind paywalls, and this generation questionable DLC practices continued to expand and mutate, culminating in the microtransaction/loot box fiasco. There was also the rise of online-only games, which will all be completely unplayable at some point in the future as the servers are inevitably shut down, a fate that all MMOs share. The generation itself started off with an embarrassing Xbox One reveal and continued PR mishaps throughout summer 2013 that suggested a radical and consumer-unfriendly change in the relationship between consumer and product. New leadership as MS was needed to reverse those initial policy proposals and shed Xbox of any suggestions of being an anti-consumer brand. This generation will probably be remembered for a host of attempted and actually-implemented practices of extremely dubious merit almost as much as it will for having a ton of solid games.
Overall, if I had to rank the already-completed generations on how they've held up, I'd say: Gen 4≥Gen 3>Gen 7>Gen 5>Gen 6>Gen 2. Gen 1 could be omitted entirely because it was all Pong machines.