Well, it might help to identify some criteria first:

1. Economics. When was it easy to just… Buy and play games? No microtransactions or season passes or subscriptions. Games were mostly physical purchases that you could buy used or re-sell.

You could make an argument that anti-consumer games have always existed in some form. Arcade games designed to sucm quarters out of pockets, games with special codes or info in the box/manual needed to progress that would deter people from buying used. Pokemon selling 2 versions of the same game and locking content behind promotional events. But all that was less common and less egregious. For some games, DLC used to be a great value because it added a lot of content cheaper than the base game- Roller Coaster Tycoon was a great example.

I think everything through PS2/GameCube/Xbox is pretty safely within this range. PS3/Wii/360 is arguable.

2. Technology. This may be controversial, but I think there is a minimum level of fidelity and performance that needs to be considered here. There are definitely some great 8-bit and 16-bit games, but there’s also a lot of duds from those days. There’s also plenty of great 2D games that came later on systems that are ALSO capable of great 3D games. So I’m eliminating anything prior to the PS1/N64/Saturn.

Except… Even just comparing that generation to the next is still a huge difference. Storage space was quite restrictive. N64 games look like garbage, and particularly with multiplatform games you can really feel how limiting the cartridge was. The Saturn was a joke. PS1 games… The aren’t bad, but there’s still a wide gulf between them and the next generation. Compare Metal Gear Solid to Twin Snakes for example, or any of the multiplats that crossed generations.

I know a lot of answers here are “what you grew up with”, but this is the point where I have to admit that what I grew up with was immediately objectively surpassed by the next generation. PS1->PS2, N64->GameCube, and Saturn->Dreamcast/Xbox were all strictly better upgrades, and the only real downside was that Xbox started charging for online multiplayer.

3. Scope. AAA games got too big. They take too long to make and cost too much money. A lot of developers saw GTA and became obsessed with open-worlds with tons of silly collectibles. Assassin’s Creed is an example, and I think the PS3/360/Wii generation is where this started, though it certainly got worse afterwards. I remember Skyrim taking hours to install, and even then the load times were so bad that my wife and I would usually be playing Pokemon on our DS’s during the load screens.

The increased fidelity also seems to correlate with a decrease in creativity. This has gotten a lot better since, but the PS3 and 360 are remembered for mostly brown/green/grey games. Everything was “gritty” and realistic. I like realism, but it was overdone here. The Wii, on the other hand, mostly just looked like GameCube games. I could be misremembering, but I think this is when a lot of games moved to target 30FPS instead of 60FPS. Trying to be more “cinematic” and reducing the importance of gameplay, and thus reducing the importance of responsiveness.

4. Tutorialization. I’m not exactly sure when this started, but it seems like almost all modern games lie on opposite ends of the spectrum. Either they hold your hand and force you to read through tons of dumb text prompts poorly explaining every element of the game all at once, or they copy the FromSoft formula and give you nothing and make you look everything up online from a fan community. I suppose older games like the OG Zelda are also known for being hard to figure out, or other games made you look stuff up in the manual. I look at Portal as one of the best at this: the whole game is basically a tutorial that slowly, constantly introduced new wrinkles for you to learn without holding your hand about it.

So I would say the GameCube/PS2/Xbox era was the peak. That being said, there was plenty of garbage released during that era, and plenty of great games released before and after.