There are some Mario titles that are fundamentally different than its predecessors. Some of them are fundamentally the same. The reason for this is because there are a lot of people who ask for the same stuff, and people who ask for different things as well. Luigi's Mansion was definitely one of those titles that has Mario & Luigi in it, but is completely different than what Nintendo has done before. I'm not sure about the horror aspect, but in terms of the gameplay itself, it bore no resemblance to their previous titles. Paper Mario was another attempt at going for the RPG in the Mario series. Changing genres is a big thing to do, and instead of Princess Peach getting kidnapped and you go through multiple worlds to save her, Paper Mario adds some twists here and there and gives the characters scripts and personalities.

Why do I hate on it?

1. Same story
2. Super bland
3. Unimaginative
4. Stuck in the past (tech allows for so much now than the past, yet you refuse to change at all)
5. Made for kids
6. Bland unengaging story
7. Milking the series'

I can go on and on about points why I learned to despise Mario as I got older. Mario died for me really with the PSO, thanks to games like Xenogears, Suikoden 2, and Final Fantasy 7. After story-telling became a centerpiece to main-stream gaming, it is hard to go back to the very simplistic way. I don't hate Nintendo though. I wish they would jump ship from the console market because I don't like what they are doing at all anymore, so it's just taking up space from sales. Just like other big Nintendo 1st party titles, they don't move on. They recycle everything about their IP's, and that is painful. You get nothing new. No new experiences. They are rehashes of the old presented as "new". Nintendo lives on this because people keep buying it (not me). Third-party developers have moved to the HD market, and you always hear how Nintendo doesn't have 3rd party support. Not a coincidence. That mentality of being okay with being mediocre and the same is the reason why they don't get support. Everyone else isn't stuck in the 90's. Make consoles for kids, it's hard to persuade grown-men to dumb down their ideas/visions to fit on a console. This is what Nintendo hardware says to me now. They are trying to get away from this though with the WiiU, but they won't commit all the way.

Being complacent is Mario's biggest problem.

The problem in the most simplistic form is they do a "reboot" like very couple years. Go somewhere else with it. It isn't about gameplay complaints, we don't mind classic gameplay. We mind being given the same rubbish for a full-on retail price. It's like being mugged. Even franchises that are done to death like CoD are given a new story and perspective after each game. If a milking factory like CoD can do it, why can't Nintendo.

I think you haven't played any Mario games since PSO, then.  N64 they released Paper Mario, GC they released Luigi's Mansion, Wii they released Mario Galaxy, 3DS they released Super Mario 3D Land.  3D Land is a retro title with a 3D platforming spinoff to it, but it plays just fine.  

Zelda titles get released quite slowly in comparison, but the new titles are always exciting to me when I see them.

I haven't really played much Metroid, so I can't speak for it.

Fire Emblem is a neat Nintendo IP.

Mario Kart is mostly where your argument I can agree with you on, but I think most people who get into Mario Kart would already know this and don't mind.

I don't think people who play those Mario games play it for the story.  The story has always been dumb, they just throw it in there to make the game look like there's a point in everything you're doing.  It's simply just a platformer though.  The games I listed are for those who want those new stories, and CoD stories are pretty BS too, and I barely know anyone who gets the game for the story.  There are also no real "character" in CoD.

Story is not important when it comes to Mario platformers, I would go as far as saying it's detrimental to my enjoyment of a Mario game. Having to go visit Rosalina in Mario Galaxy was a low point in the game, all I wanna do is explore the new worlds.

Yeah, I didn't really pay any attention at all to the Super Mario 3D Land story and it was still a good amount of fun for me.

I think part of problem is Mario being in the game means creativity will be limited to Mushroom Kingdom norms just applied to new Sport title like Basketball, Baseball, etc.

I mean I enjoyed Sega Soccer Slam and heck of a lot more because all characters and gameplay was fresh and awesome... but Mario Strikers from same developers sold a ton more.

So why fresher IP can be more fun, familar IP sell more.... at least for the family games market.

Nowone wanted to LOL with me on mom loving plumbers.

Okay...

There are similarities, that is the nature of a franchise. You wouldn't make a a Final Fantasy game that was all about Kobe Bryant's adventure into the NHL.

However, saying Mario has limited creativity is a HUUUUUUGE inaccuracy. Mario Galaxy 1 and 2 are two of the most creative videogames ever developed. The franchise is the most creative of all the major franchises from throughout all of videogame history.