I cannot in good conscious think that the improvement between the first generation of Atari 2600 games as compared to the last generation of NES games isn't by some magnitude more substancial than the relative difference between the same eras of PS3 and PS4 games. If those later games feel like they seem to take longer to become retro I think there's a reason.
I kinda feel like game design sensibilities haven't change that much since the PS2 era (6th gen?) -- where the "final controller" coalesced. These days, evolution seems to be more focused on how to monetize things.
My personal "retro" cutoff is 5th gen (PS1/N64) era, because the early 3D game design of the era feels pretty distinct from the stuff we started seeing from 6th gen on.
If I was just going with my at-the-moment gut feeling and trying to draw just one line in the sand "developed to play on hardware that has in-built support for polygonal graphics" would be where I'd put it, yeah. Give or take a year or two for the weird standardization of all controllers/generally universal PC/console benchmark and associated normalization of ubiqitous multiplatform releases.
That being said, I have always been of the opinion that the whole "Xth gen" terminology is totally worthless, arbitrary, and confusing. Like if you really really want to insist on a numbered system based on console releases, it would actually make more sense to count by Playstations and just accept that you're going to call the period where it was all about the SNES and Genesis "the PS0 generation" and the NES' reign "the PS negative 1 generation" and... honestly the fact that prior to that it was kind of just the wild west is why it's so damn weird that we're claiming 2 generations existed. That part really feels just backfilled from the 7200 technically being around at the same time as the NES except wait the 2600 and 5200 are both "2nd gen" and "1st gen" is just various closed-box Pong clones.
If you really want to look at things from a historical perspective, I'd think the thing to do is focus on points where developers had and noticeably used new options on the table, and accept that there's going to be a lot of parallel threads running up until... basically the release of the Switch, honestly?
So just offhand...
Early Electronic Games- You have videogame things that are really one-offs not proper consoles, and for resolving corner cases I don't actually care if you technically have swappable cards/carts/boards until we're loading them up with ROMs significant enough that we're porting Asteroids/Space Invaders/etc. to the format. Furthermore there's no requirement here of a CRT being involved. If you wanna call oldschool arcade light projector gun games, pinball tables, or Operation early electronic games, cool.
Early/Pre-Crash/In-House Consoles- Basically everything predating the NES goes here, and that actually should probably include at least the earliest Famicom games. This is the period where hey, this arcade game is really popular. Let's allow these people making home game consoles have permission and whatever notes we have lying around to code ports of it to their things as best they can.
3rd Party Console Development- The start of where developing games explicitly for consoles, rather than just porting things to consoles, really became a thing, particularly but not exclusively with the Famicom. Very notably, here's where Capcom and Konami really started doing their things. Less score chasing, more exploring going on.
FDS- At this point the Famicom is pretty much The Console, and here comes The Add-On that let people do stuff on it beyond the initial capacity and in particular, get kinda sprawl-y and save-and-come-back-later with design concepts.
Cart-Cramming- There's a pretty clear line where Famicom/NES games with extra/better guts started displacing the FDS, and while it's harder to see from North America where we kinda started here and got a bunch of old ports mixed in, it was a real clear game-changer in terms of what could actually be done and where the bar was for complexity and amount of content.
16-Bit- Straight-forward enough I don't need to elaborate.
Media Transition- There might be some other significant milestones I'm just not aware of, between this and the last one, but there is a point where CDs and laserdiscs were really catching on, along with people getting their toes wet with 3D modeling, wherein we had a lot of failed launches of new disc-based consoles, add-ons for existing consoles, and games being designed for things that never came to be and compromised in interesting ways. Plus the whole pre-rendered graphics look.
Early 3D and late 2D- Here's the big proper PSX/N64/Saturn jump, where everyone was making either the same sort of games they were previously but with broader color palettes and they're probably like 100 hours long or full of splashy cutscenes, OR they're diving in with 3D, trying to work out how that works, not really bothering with textures, really experimenting a lot with basic approaches to level geometry and how-do-I-even-camera.
3D Standards Established- Or, Every Game Is Now Ocarina of Time, Final Fantasy 7, or Resident Evil. I don't mean that derisively, but by like 1998 or so, everyone pretty much got in lock-step that you move with the left stick, adjust the camera with the right (PS there are sticks now), use a shoulder button to lock onto a target, always put textures on every polygon, hide pop-in with fog, and you either walk a relatively high poly character around on some pre-rendered scenes or you run around in full 3D cribbing everything you can from the UI of the first game to really establish how that's done. Also we have a really really codified list of genres, and nobody's trying any weird Tail of the Sun type stuff anymore.
Everything Is GTA3 Now- Or, [placeholder for if I can find that "Driving Sections! Shooting Sections! Stealth Sections!" video again]. Early games for the PS2/Gamecube era of things really weren't meaningfully different from what came before except for maybe looking a little cleaner, until GTA3 came along and then literally everyone was just going for that "open world" kitchen-sink approach and all the genres kinda collapsed into this mush of 3rd person action with RPG elements and maybe first-persony shooting and you probably have a car or at least a horse and they're kinda still that now and we call them "Triple A Games."
Everything Is GTA3 Now- Or...
Early games for the PS2/Gamecube era of things really weren't meaningfully different from what came before except for maybe looking a little cleaner, until GTA3 came along and then literally everyone was just going for that "open world" kitchen-sink approach and all the genres kinda collapsed into this mush of 3rd person action with RPG elements and maybe first-persony shooting and you probably have a car or at least a horse and they're kinda still that now and we call them "Triple A Games."
A BIG SCHISM HAPPENED HERE
No I said OPEN WORLD games!- Or, Vast empty brown fields of rocks, which you can use as cover! As we all seem to agree things have been really really stagnant since controllers were standardized and draw distances pushed out past like, 15 feet, so the next points of interest I can think of is the jump to the PS360 establishing DLC as a Thing, which had a pretty profound effect on how all nearly games are designed, and the big push towards just having stupidly huge world maps which it's tempting to pin on Bethesda but I feel like Assassin's Creed where the industry went "yeah, this is the thing we're doing now."
Games As Service- Big ol' shift to doing all kinds of stuff server-side, even in theoretically single-player games, lootboxes, chasing that Battle Royale trend, matchmaking algorithms, etc. You are here. Which is impressive because I think we've been here for like 2 and a half console generations now.
... however, getting back to that big schism! While everyone who generally kind of "identifies as a gamer" has been over there with the universal controller standard and the Action-RPG-shooter-stealth-explore'em-ups, most people, generally, took the other path.
Stomp and Shake- DDR was kind of huge, and lead pretty quickly into your Sambas del Amigo, your Rock Bands, and of course, all that Wii shovelware (plus Wii Sports which is great and you know it's great).
Home Mo-Cap and AR- Somewhere on this branch, people got sick of all the plastic instruments, and decided to see what could be done with cameras instead. So you've got the whole Kinect thing happening, the eyetoy, a bunch of stuff with the 3DS camera you were blown away by when you first got it and then totally forgot was a thing. This sort of stuff is still going strong.
This would lead to another clear era here, of VR gaming, but... broadly speaking nobody actually seems to really want that except for neo-nazi venture capitalists really really aggressively pushing specific hardware that costs too much and strangling put-a-cellphone-in-a-cardboard-box technology in the crib.
And all that's just consoles! I'm less qualified but chopping up arcade boards in a similar fashion makes sense, plus whatever was going on in the PC gaming scenes in the UK and on the MSX, which I doubt map particularly well to consoles, or eachother, or the DOS and Apple ][ scenes, and it's kinda really important with any sort of look at game history to very explictly note when Wizardry happened. And then there's the whole history of FPS games and notable engine developments there, PC OS boundaries, whenever it is when we stopped having 20% of the screen be the game boxed in by really ornate UI elements and maybe the title of the game, maybe just a big hot girl in there somewhere, or some skulls.
