Now is not the right time to radically change the formula. Lots of people on Switch did not get to play the original Splatoon, an iterative sequel was the right move.

Splatoon 3 can take bigger risks in terms of changing things, but right now IMO it would not have been appropriate.

In general I think sequels to competetive online-centric games are more difficult, because the more you change the higher the odds are you are upsetting the balance of what people liked about the game in the first place. When I play basketball, I don't want to show up to the gym finding out the rules have changed, and now you can take 4 steps instead of 2 and the there's a 8 point shot or something. 

I think it was mostly because they did not have much time to make the game.
Splatoon 3 should have both the budget and time, as well as the fanbase to support a more ambitious title.

It's a good sequel and better in every way than first game.

No, it is far too similar to the previous game.
It is closer to a remaster with some added content.
A sequel is suposed to build on the previous game, not be the previous game.

I thought you said you didn't play the first game?

Imo, it's worse. Nintendo has deliberately done to Splatoon what they did to Mario Kart. They've dumbed it down and made it easier for people without any skill to do well. I really enjoyed the first game because it rewarded defensive players. It felt like Halo 1-3 with a Nintendo coat of paint. Now, it feels like COD where it's more he-who-shoots-first-wins. I hate twitch shooters and this game is way more twitchy because they've removed defensive abilities from the game and altered the hit boxes.

I did watch the story mode from the first game, and watched some multiplayer gameplay.
You don't need to dig too deep to see that they are quite similar.

The graphics look a fair bit better, and the multiplayer / story has been remixed.
Splatoon 2 is not an evolution of Splatoon.

Never played the first one. The game itself is great though so I don't see how people can be disappointed.

I need to mention that I haven't played Splatoon 2 yet, but from everything I've read and seen it seems to be pretty much more of what the first game was. The gameplay seems to still be very good, but the game itself is hampered by some really stupid decisions regarding things like the availability of the game modes. The modes themselves are apparently a lot of fun, but making them accessible only sometimes is just pointless and ultimately makes no sense.

I guess it depends on how you view the first game as well. The first game didn't have Tower Control, Rainmaker, Private Battles, etc. until later down the road after initial release. Splatoon 2 already has all these modes day 1, plus league battles, a new story mode (which I think is better due to the more variety of weapons being used), and Salmon Run. So if you compare the first game with all its content, then I guess you can see some of the complaints of similarity. However, the vanilla version of Splatoon 1 is easily trounced by the vanilla version of Splatoon 2, with much more coming as we already have the Splat Brella added now. The devs stuck with the same strategy of updating the game with new weapons, stages, etc. consistently so it can be hard to judge fully until the last update of 2 is shown.