The problem is, Mario used to be a different game every time it came out. There were common themes (Reach the end of a level, collect stars, Bowser kidnapping Peach, etc.), but the music, settings, gameplay and art style would always change, making it a fresh experience.
Now we have 4 games that look alike, and 2 Galaxies (so far). It's troubling for long-time Mario fans.
"Troubling" for long-time fans? Ever since SMW, we've had to wait entire console generations in between games. The next Mario game after SMW was Mario 64, and the next Mario game after that was Sunshine, followed by Galaxy. We're lucky that Nintendo have been putting so much effort into the series since the Wii, if anything. Super Mario Galaxy and its sequel are amongst the best 3D platformers I've ever played, despite falling short visually, NSMBWii was a lot of fun to play alone and with friends, and from what I've played of Super Mario 3D Land was great.
The problem is that Nintendo have been pushing out too many NSMB games since the Wii one, with two sequels following it. They're likely cooking up a brand new 3D adventure that's as big a leap from Sunshine to Galaxy. I don't see what the problem is when Nintendo have been putting more money into Mario platformers than ever since the Wii's release.
I concur. Seriously, the gap between World and NSMBDS was like 15 years. It's a nice change of pace to finally see a bunch of Mario games.
^Huh, I wanted that on the contrary. Besides, we did have a gap in Mario Party games.
I don't think it's an excuse for Nintendo to shell out more of the same Mario games just because of a gap in the Gamecube era.
The NSMB games are the only games that share too much in common with one another. Galaxy was a completely new experience, Galaxy 2 offered completely new concepts and ideas in every single stage, and Super Mario 3D Land is its own beast. That's 3 original, 3D games in one generation, and they're likely cooking up another one for the Wii U. Nintendo are catering to every possible Mario fan at once, I really don't see the point in complaining.