Simple, because the Mario series is expected to have the same formula, Sunshine has a similar one but many people think it was made really kiddish, first with the title (Sunshine everyone?), then the vacation plot, then the cleaning message, etc... Most Mario fans want the series to have the traditional formula (Like in New Super Mario Bros, and the sales don't lie), or at least the formula with changes that don't mess with it (like 64)...

Now, i'm cool with the game, i'm just transmiting what some have told me...

It was a great game, in 90% of all game series, it would have been considered a top of the line game, but as a Mario game, not so much.
The story was stupid and it took way too much time to tell it. Super Mario 64 handled the story and the storytelling much better.
What was fun in the game, was cleaning up the stages, where FLUDD felt like being useful, beating Shadow Mario and the levels where you didn't have FLUDD. Too bad those levels weren't the majority of the game.

Overall the game wasn't bad at all, it just wasn't up to par with other Mario games.

I loved SMS! Here is how I would rate the games: SM64/DS:9.9 - SMS:9.8 - SMG:10

All 4 are brilliant and very fun games!!

I loved it.

There is nothing wrong with SMS. FLUDD added more gameply elements. and the level design was awesome.

I liked it from the videos I saw. I plan on buying it soon.

i love Galaxy,but never played Sunshine, if it's such good (i know it is)....
is is coming along with Pikmin and Metroid with Wii Controls!?

I never hated it - it is an excellent game, and a solid 9 for me. Its also extremely hard (never finished it 100%, as I did Galaxy).

My gripes with the game were simple: it lacked polish. It felt inconsistent - some stars took forever to finish, then I would blow through 3 or 4 in 10 minutes.

And the entire setting pissed me off. It wasn't that it was new - it was that it didn't use enough of the "classic" Mario as reference (classic enemies, giant mushrooms, etc).

I felt that the game was "rushed" - which astounded me considering we had all waited 6(?) years for another Mario game.

I really enjoyed the water spray mechanic, and the "cleaning" mechanisms - excellent gameplay. But it did take away from the classic Mario platforming (which didn't help that much). The bonus levels were excellent, just too hard in places - the normal game was generally too easy.

Overall - still a 9, just not quite up to the standard set by Mario 64 (which was VERY high...).