I didn't count the advance series because they're remakes and Wario Land 4 is not a standard Mario game, Wario land is its own thing.Super Mario Advance even if that was a remake. Wario Land 4 as well.They are portable titles, there haven't been a good original portable Mario platformer since the land series on the original gameboy. GBA didn't even have one.I think that nintendo is over-using (sorry about my English here) the Mario franchise more than anytime before, and none of these games are "spin-off" title, witch made the situation worse.
I've always counted the portable games as spin-offs since NSMB DS was released.
Scratch that, I've counted portable Mario platformers as spin-offs since the first game in the land series.
New Super Mario Bros. was still pretty good. Even if it wasn't the pinnacle of Mario platforming, I enjoyed it.
3D Land is stellar and New Super Mario Bros. 2 is good despite the lack of innovation.
About NSMB DS etc.
I'm not saying they're bad games but they didn't really bring much new content to the franchise compared to the other games. I still enjoyed NSMB DS for what it was.
All I'm saying is that people shouldn't expect much from a handheld Mario platformer since they've historically never performed that well to say that they're mainline Mario games.