As the title says. These are games that came within the first 2 years of a generation/console that announced in their technical abilities and visuals why they justify a new hardware generation. Console or handheld.

1990 MUSHA on SEGA Genesis/Mega Drive. Esp in the US. Most people were used to NES. This game blew people away with it's speed. The detailed sprites. Parallax scrolling. Music. Some stages giving off a 3D look as you look down below clouds or a massive cliff. Hard to see now being 34 years later. But this game turned many heads back then. This is back when COMPILE was one of the ace developers along with Toaplan, Tecnosoft, and more and not making loli crap.

Shenmue in 1999.  Shenmue had focused on big areas but not the open world. Still insanely detailed with great character models with lip sync. Individual fingers are carefully modeled and textured. Random weather. Taking individual objects out of drawers. Off shelves, Off walls. Lights had a pull cord that would have perceived physics on the cord after being pulled.  This was the first time I ever saw a console game exceed PC visuals despite the power difference. It was also the console that for the first time I saw exceeded arcade hardware in Soul Calibur. I thought about including that game but Shenmue blows it out.

Great idea for a thread. There are a ton of excellent examples.

The ones that stood out the most to me are:

F-Zero

Mario 64

Rogue Squadron II

Halo: Combat Evolved

Gears of War

Gears of War, definitely. And while it came more than a year into the generation I'd say The Witcher III too.

GT3 and MGS2 they made dreamcast games look last gen

 MGS2 nah. Never was impressed with it. Had that PS2 blurry hazy look and low rez textures. No I'm not going to debate this for 10 pages and no you are not going to derail.

Oh it's definitely GTA 3 on the PS2

It's ok you weren't impressed, everyone else had their jaws on the floor and this is someone who owned a dreamcast, and even i had to admit it blew everything on dreamcast away

The Legend of Zelda: A Link to the Past. The rich color, beautiful soundtrack, and smooth controls were miles above anything the NES was capable of doing.

Metroid Prime. Made most PS2 games look last-gen.

Super Mario 64, for obvious reasons. Probably the best launch title in history except perhaps for SMB on NES.

Yeah, it was impressive for the time. Funny development began on Dreamcast (same with ZOE 1 from Konami) but ended up on PS2 for obvious sales reasons. Devs were confident it would run just fine on DC. Fans right now are porting it.

That said.

 Since Gears was mentioned. Dead Rising. All those zombies are on screen at once. Impressive. Going back to PS2. Dynasty Warriors 2. Similar reasons. That era of gaming was devs showing off hardware by how many things/NPCs can be on screen at once. DW2 with all that on screen at once.

The GTA 3 port looks horrible so far on dreamcast, but it's still early let's see what the end result is.

On ps4 it was star wars battlefront and order 1886 they blew everything away.