You could take a game running on the most powerful of commercial PC's at the time of Link's Awakening, something like:

or a 3D game on home console:

and the comparison is just as astounding.

N.E.S.: Super Contra. It was such a badass game I remember crying with joy while playing it (I was like, 7 or 8).

S.N.E.S.: Kirby's Super Star. I never played a game so diverse, so complete, so excellent in every single way. The soundtrack, the co-op, the design, and of course, the hats! Still my favorite video game of all time.

N64: Ogre Battle 64. It was well beyond my expectations. The music, the overwhelming story, the strategy required, the replay value. It was a game that completely took my life by storm.

Gamecube: Obviously it is Metroid Prime. I was in Circuit City and saw my girlfriend start the demo on display in the Gamecube section. Until I saw it in action, I was against Metroid going first person. Less than two seconds into the demo, I was walking to the register to pay for a game I had absolutely no intentions of ever buying.

Wii: Probably Wii Sports. It was the moment I realized my 5 year old daughter, myself, and my 45 year old mother would all be gaming together. And it is a game that has withstood the test of time.

Wii U: Call of Duty. To be able to play it in HD with pointer controls... ...and then to play multiplayer without splitting the television screen. It was a mind blowing experience.

Switch: Implosion. It was a game that looked great on phones but I struggled to play because of the controls. However, the Switch version actually made the phone game feel like it was designed to be a home console experience. Still captivates me to this day.

So this is just consoles, no PC, no handhelds no arcade games. Those have wowed me too but they aren't defined the same way as console generations.

Gen 2: This is a bit weird, I didn't have a gen 2 console but I did have an Atari 7800 which played Atari 2600 games. I didn't even realise it at the time but I guess looking back, if I had to choose my wow moment from that selection of games it would be River Raid. Not for any really impressive reason, just that it was maybe the only 2600 game that I owned that I really liked. It was the first scrolling shooter I ever played too.

Gen 3: SMB3, the whole game just blew my mind with all the secrets and variety. Sometimes a coin ship would appear, or you could fly over a level and find a warp whistle. There were giant enemies and the game goes up into the freaking clouds. Oh and there's a frog powerup. Kirby's Adventure is the other contender, more powerups than Mario 3, saving, the ability to revisit levels and graphics that seemed like they could be on the SNES all helped to make this my favourite NES game at the time.

Gen 4: Either Sonic the Hedgehog or DKC both seemed unbelievable. Sonic had a pseudo 3D look to it's background with the parallax scrolling water effect in the first level, the speed and different routes felt completely new. DKC just looked and sounded unbelievable, it looked like the next gen to me.

Gen 5: I think it's Virtua Fighter 2, seeing the intro with the 3D fighters made it seem like consoles could now do anything, it also had something that just looked so good that I would eventually identify as 60fps (or 50 I guess) years later. FFVII is another contender not so much for CGI cutscenes, but for allowing them to flow seamlessly into or out of gameplay. Also for showing me how massive a JRPG could be. Mario 64 would be the last contender, although later than VF2 and other 3D games, it showed how my favourite genre at the time could be done in 3D. On a non technical level FFVIII just absolutely wows me to this day, FFVII laid the groundwork very nicely and then VIII just improved everything from tech to the game as a whole. My favourite game ever.

Gen 6: Probably Gran Turismo 3, the graphics and smooth 60fps (yeah it was really 50 again but 50fps on a 50hz screen doesn't seem weird like 50fps on a 60hz does) seemed like more than I could possibly have hoped a console could deliver. FFX really impressed me too with the seamless battle transitions and much improved graphics/animation and Jak and Daxter had no loading times which I was amazed by.

Gen 7: Maybe Uncharted 2, the graphics and animation were very impressive and I thought it was a true leap ahead of the last generation. This generation was where I began to think that the real leaps forward were over, so I find it harder to think about what just seemed unbelievably impressive.

Gen 8: At first I thought this was going to be difficult because although a lot of PS4 games have been impressive in one way or another, none really stand out. FFXV did get me excited when I saw the car taking flight for the first time, Spider-Man also impressed me for various reasons but then I remembered the real wow moment and it's a big one. VR, specifically the PSVR has wowed me like some of the earlier gens. It really feels like a brand new way to play games. The standout moments for me so far have been Driveclub on day 1, were I just sat and looked around my car for ages looking completely stupid to others in the room, Wipeout felt like the moment where I fully appreciated how VR could actually enhance the game past the novelty and Astrobot filled me with joy at how VR could be implemented into another genre.

True that, or to take things a step further, that the best looking handheld games look better now than the best looking console games did just five and half years ago.

Thank you, I think that's about all I need to know about the game (in a good way)! 

I'll certainly try it, most likely sooner rather than later! I actually was getting somewhat invested in it - then I had to start my DMC marathon in time for 5 Maybe I'll play it with or after Sekiro. 

The funny thing is that I already knew you could play as other characters - but I thought it was basically completely superfluous, basically kind of like trying to enact old JRPG mechanics into an action RPG for the sake of adding diversity to the player model. Now that I know you can play as more than one character in "campaigns" of sorts, I'm wondering if that other really popular 3rd character ... A2 or something like that? ... is playable. 

Either way, I'll try not to spoil myself, and to at least get farther in it then I have before, next time I try! (and unfortunately I'm going to force myself to start from the beginning for the 21st time ... for the sake of context and mood : P ) 

These wow moments don't necessarily mean the games listed have the best graphics or gameplay of the generation to me. Just that I was wowed the most at the time. (edited formatting)

Gen 4:

Graphics: SNES - Donkey Kong Country
PC - Doom
Arcade - Mortal Kombat

Gameplay: SNES - Street Fighter II combo system

Gen 5:

Graphics: PS1 - Tekken 3
N64 - Super Mario 64
Arcade - Time Crisis 2

Gameplay: PS1 - Ape Escape control scheme (though Klonoa: Door to Phantomile is a close second just for the ending)
N64 - Super Mario 64 platforming

Gen 6:

Graphics: PS2 - Ico
Gamecube - Tie between Super Mario Sunshine (water effects still look great) and LoZ: The Wind Waker
Xbox - Dead or Alive 3 ("physics")
PC - Half Life 2 (didn't play until a generation later, but saw gameplay during the generation and was floored)

Gameplay: PS2 - Three way tie between submarine level of MGS2, battle with The Boss in MGS3, and beating Dynamis/gaining entry to Sky in FFXI...uh, and I keep thinking of more wow moments. Ico, Shadow of the Colossus, God of War. PS2 had too many to choose a favorite. And all these games had wow moments in graphics, too!
Gamecube - All of Metroid Prime
Xbox - Playing Halo 2 online against friends

Gen 7:

Graphics: PS3 - MGS4
X360 - Gears of War
Wii - Super Mario Galaxy
PC - Crysis (again, didn't play, but just saw footage)

Gameplay: PS3 - Ellie vs David in The Last of Us
X360 - First puzzle with both portals in Portal on The Orange Box

Gen 8:

Graphics: PS4 - Infamous: Second Son
PC - Metro Exodus (again, didn't play, but just saw footage)

Gameplay: PS4 - All of Bloodborne (and the art direction still blows me away despite the graphics not being the greatest)

Playing Pong for the first time back in 1975 when I was 10 years old blew me away, that's#1. Lived through the Atari, Intellivision wars. Arcades were better. Ever during Nintendo's early console days, arcades were better. The PS1 and to a lesser extent the N64 and too many games to list from that era would be #2. No era for me has topped the PS1 N64 era.

On Gen 6: GTA III and Vice City. Those games wowed the hell out of me when I first saw them. I went to my cousin's house to see they had GTA III and I was mindblown by the level of freedom compared to other game I was playing a lot back then, Driver 2.
On Gen 7 there were a couple of things that surprised me. Call of Duty 4: Modern Warfare was one. It was a massive leap over the previous games of the franchise and a good way to establish itself on the beginning of the generation. Another thing that wowed me was the MGS HD Collection. A collection, you ask? Yeah, but it had two games I really liked and one game I tried and still love to death to this day, MGS Peace Walker. It's amazing how far they go for remasters.

Honorable mention to Wave Race 64 and that totally realistic water.

Well, at the time it was real...

Ah yes, excellent pick.

I remember being wowed quite a few times by water in video games.

Banjo Kazooie, where it undulated and where the drops from a splash created their own ripples.

Blinx 2, which I got with my original Xbox, which not only had an interactive 3D water mesh but when you froze time you could carve it out of the way, only for it to splash back in to fill the gaps when time resumed.

Mario Sunshine, Starfox Adventures, and RE4 on Gamecube. The TEV hardware in GCN/Wii was quite good at doing nice looking water.

The ocean in Crysis. Like so much about the game, it looked mind-boggling real for the time.