If by niche you mean biggest and hardcore you mean everybody, sure.
Sony is gonna use everything they have to throw Sackboy at the world and make everyone love him. Will it be a succes? everyone that consider themselves a gamer should hope so. In this case i will be stupid optimistic and say it will be this generations number one title. Much more fun than just being angry and negative.
I don't agree. While the game thankfully ships with levels after that its up to the user to find more and we can see from youtube and other services that there is a lot of poo to go through before you find the gems. I don't think the casual market is going to go for that. This isn't wii fit or wii sports. Its a 2d hardcore platformer.
I also don't get what you mean by this being the generations number 1 title. Do you mean sales wise ? If so you think this is going to beat halo 3 and gears of war and wii fit and smash brothers ? Or do you mean the most sought after game, which i don't believe for a second as I never hear any talk of this title outside of these forums. I know sony has been pimping this for a long time but I just don't see it happening.
Honestly though if you want to argue about this we can do this in the LBP thread. I will buy the game but i've stated I don't know if sony is going to be able to make this game right and if they can handle all the dick and fart joke levels that get thrown at the title by users