Obviously not. If most people cared then they wouldn't buy the games. If people didn't buy the games then Nintendo wouldn't continue to make them.
If you have a forumla that works, why would you risk alienating your core audience by trying to innovate and make it different? That's what spin-offs and sub-franchises are for! When I buy a sequel to a game, I'm wanting more of the same... a few new gimmiks, imporved graphics, and different maps, but I absolutely don't want a completely different game. I imagine if a NSMB game came out where the game mechanics were totally different to the previous ones there'd be a public outrage.
You said it right there: Sequels. Of course people want a sequel to be an expansion of sorts to the original games but the Mario series isn't a series of sequels. The NSMB games are all sequels to one another, and that's why they're all the same. 3D World is a 3D Land sequel, and that's why it's also the game. Galaxy 2 is a sequel, and that's why it's the same as Galaxy 1.
But that's the problem - There's too many damn sequels.
Super Mario Bros. 2 isn't really a sequel to Super Mario Bros. 1. The real sequel to Super Mario Bros. 1 was Japan's SMB2, aka The Lost Levels - which, obviously is the reason why it was the same as SMB1.
Super Mario 64 isn't a sequel to Super Mario World, despite the fact that it was the next main Mario title in the line.
New Super Mario Bros. DS isn't a sequel to Super Mario Sunshine.
Super Mario Galaxy isn't a sequel to New Super Mario Bros. DS. Super Mario Galaxy 2 is.
The point being, just because it's one franchise, it doesn't mean every game has to be a sequel. The next game in line isn't necessarily a sequel to that game. The first eight Mario titles were all super original with their own defining characteristics. The second eight Mario titles were
all sequels to a previous game, with the exception of 3D Land.