The Japanese release date tweet for Splatoon 3 is now the third most liked gaming related tweet ever. They sure do love Splatoon over there.

https://twitter.com/SplatoonJP/status/1517488719900536832?s=20&t=a57BClKcD7YX7JMwZkIrfQ

I'd hardly say Mario Kart and Smash "reinvent" themselves with each entry. They're also iterative sequels that generally carry on a similar gameplay to what the series is known for, however they have a different feel each time because every game is made from the ground up. Never mind the graphical disparity between each one, the way everything controls feels different because each game has a different engine. I remember being really weirded out by Ultimate at first after so many years of Smash 4, my first few games I felt like I never played Smash before because the way everything moved felt so different. Whereas the first time I played Splatoon 2, it was basically the same feel as the first one, just different weapons and stages and stuff. But the physics and movement of the game were the same. I thought it was fine and acceptable for what it was, but really hoped that a third game in the series would bring more with it, and instead were getting another game clearly built off of the same engine with the same base mechanics.

Uncharted is single player. I think this a pretty relevant distinction. A multi-player game, a PAID multi-player game I must adress, needs a reason to abandon the current game and go buying the next one. Majority of Splatoon userbase will spend their time playing multi-player matches hence you need stronger reasons to get the next installment. 

And Halo is... I will refrain to say what I think about it because I don't want to start fights here

For Splatoon it don't need to be once per generation, but still lacking some substance for a sequel. Nothing I've seen so far is compelling me to get the next one, I see no major improvements in graphics, in maps or in gameplay. I've seing new guns, couldn't any of that be in Splatoon 2? I'm expecting this one had more multi-player options (or simply different options) aside of Turf War and Salmon Run, and/or new matches to play ranked other than the currents ones (Tower Control, Splatzones, etc). Is this is fulfilled I will embrace Splatoon 3, otherwise I will keep playing Splatoon 2 for as long I'm able to find matches 

Splatoon 3 is on the same hardware as Splatoon 2 so I'm not sure why you'd expect the same kind of graphical upgrade as franchises that release once per console, that's physically not really possible.

See my answer to Icaro below as far as new additions.

So far I think they've shown plenty of additions. Just from the trailers so far, with Nintendo being rather coy:

- A cool new setting in the Splatlands and Splatsville
- The campaign being played with a Salmonid buddy almost Banjo-Kazooie style
- New moves like the Squid Surge, spin jump, and launching to the map instead of spawning on single fixed spot enhance mobility and give more options on the battlefield
- New specials like the Zipcaster similarly giving new tactical options
- Snippets from the single player teaser show bigger and more open areas than 1 and 2 like the icy launch site
- The new music has a rock vibe that is both distinct from and to me an improvement over the musical style of 2
- UI, graphics, and overall presentation has been tightened and buffed
- The tease of what appears to be a kaiju-sized Salmonid in Salmon Run
- Throwing eggs in Salmon Run is a significant QoL touch that will change the flow of play
- A new enemy teased in the "mammalians"

The fact we haven't even seen the new idols yet suggests there is plenty left to be revealed too; this is the company that just recently revealed one of the central hooks of Kirby and the Forgotten Land, Mouthful Mode, two months out from release.

Altogether, that's enough for it to definitely feel like a sequel to me, as someone who really enjoyed Splatoon 1 and 2. The gameplay tweaks alone would change the fundamental gameplay of 2 too much to just be added to it as DLC.

Errrr. You made a pretty bad list of content that are supposed to be enough to yields a sequel. I'm mean, I understand they have a new hub but... who cares? I don't play at the hub. Music and guns can be added trough DLC, and so new maps 

The point that is the most compelling so far is that you have a new set of abilities and therefore the older maps and weapons might not be balanced and adjusted to accommodate those new mechanics, however are just a new set of abilities enough to justify a purchase of a new game? For me, nope 

I know they are saving more for the next trailers, that's why I'm still interested in Splatoon 3, but I'm expecting them to display more than new maps and weapons. New Turf War rules/dynamics, more/different ranked battles options, more/different co-operative game options like Salmon Run.  This is what I look for, things that make me play this that I couldn't play in the game before. The other things are mostly nice added cosmetic details which I like, but alas, adding a "new kind of enemy" is not enough for a sequel