Too kid friendly. First off, you can take the Resident Evil and Manhunt franchises and shove them up your ass. Their problems are a completely different can of worms.
There are a handful of good M rated games on Nintendo systems, emphasis necessary, but that doesn't mean they appeal to mature audiences. Look at their best selling and top rated games. They're mostly first party, rated E, sequels, and some are better on other consoles. I've owned most Nintendo consoles with the exception of the SNES, DS, Virtual Boy(shudders), and GB Advance.
Too casual. One of their bestsellers is the dog simulator Nintendogs. It's almost like having a real puppy but you can kill it with moral ambiguity and it doesn't require real food or you to get off your fat ass to exercise it. Nintendo isn't a stranger to requiring its gamers to exercise. It's not a bad thing getting brittle, fat, and lazy gamers like myself out of our recliners.
What is bad is the utter lack of immersion these games offer. Look at Wii Boxing, it's fun, takes some energy, but loses me when I remember I don't have fists floating a foot away from my body like Rayman. Their best games might be fun but take no real skill to play and win... I'm pointing at you Mario Kart with the fucking blue shell and lightening pieces of shit.
Franchisicide. No matter whether it's a handheld or a console, you better believe there will be at least one rendition of their flagship franchises. There will always be a Legend of Zelda: [Insert Subtitle Here], Metroid, and Super Mario Whatever. That's the case with most manufacturers. Microsoft has Master Chief and Sony has... let's just say Solid Snake and wash our hands of it. The difference between them is at least when Sony and Microsoft reinvent the wheel they do it with slight progression and say "we've got a mighty fine wheel here, yet again." Nintendo on the other hand just gives you the same wheel but claims that it can now roll forwards and backwards.
Mario. What a sell out. He has soccer, baseball, tennis, golf, fighting, and kart racing games as well as platformers in 2 and 3D and a fistful of others that I don't care about. No doubt he is the face of Nintendo. I'm Greek so naturally I have a general distrust of Italians. What I'd really like to see is the real Mario. A plumber with a chest full of hair seeping out his unbuttoned shirt collar, gold chains, a drinking problem, and an undeserved feeling of accomplishment every time he beats the princess for not making his cake properly. Now that's a game I'd play.
Fanboys. My name is Jimmy and I'm a recovering Nintendo fanboy. Altogether, "Hi Jimmy!" It's been one console generation since I tried to defend Nintendo for no good reason and... it gets easier to not do it all the time with all the puke faces out there willing to do it for me.
It seems whenever Nintendo releases a first party title there are slews of people willing to purchase and defend it with reckless abandon. Never mind it treks the same ground as every other game they have or that it lacks substance and the semblance of an original story. I hate fanboys!
Lack of real technology. A touch screen is hardly new technology, neither is a motion sensitive controller. Though it is innovative, it certainly isn't new. I don't like Sony, but at least they put a Bluray drive in their console and let's face it, the PSP should be the leading handheld if not for all the children and Japanese girls. Microsoft doesn't have anything as technologically advanced as Sony but Live is the benchmark that all online games must adhere to, including the snobbish better-than-you-console-playing-peasants PC games.
No widespread online support. Mentioning Live reminds me that there are some online Nintendo games, but there isn't a friends list nor any widespread support. Nor are there millions of players waiting to go into a game. They certainly don't have any extra content to milk more money out of my pocket, but I can point at Rock Band and say that's a game that deserves downloadable content.
Downloadable content was initially and is increasingly a rip off, also another can of worms, but it lets players have a reason to play old games again. I would be all over new courses for Mario Kart. This is an area that Nintendo has dropped the ball and is alienating players and developers.