Having actually played through a recent game for once, I'll add in my two cents. About 6 or 7 months ago, I finally bought and played through NSMB Wii. I'd played a couple levels here and there with different friends who owned it but it never really engaged me that much. However, once I started from the beginning, I started digging it actually and coming to like and respect the game. I completed the whole thing in about a week playing a bit every day that week because it was rather addicting.
Flash forward to last month and I thought I'd play NSMB2 expecting it to be a shorter playtime like NSMB Wii and cut through my backlog. While it didn't take that long to complete, (I'd say about 2 weeks playing it off and on although I'm not even close to getting a million coins), I found it a struggle to complete as it just didn't engage me or interest me as much as NSMB Wii. I think it has something to do with the hardware. The Wii had moving ground and hidden caves and yoshis and other such goodies. NSMB 2 doesn't have many of those features and plenty of beanstalks instead which was disappointing. I'd play a couple levels and almost have to force myself to keep playing at times. Some people like the coin rush aspect of the game and that will be how you get your million coins but for me, I'm not an arcade type player where the goal is to get as high a score as you can. I just don't see myself really ever going back and playing this game through again like other Mario titles such as World, Sunshine or even the original.
I have started playing Super Mario Land 3D however and that is the better order to play these games. 3D Land is so odd and different and yet strangely very right. I may end up derailing this topic talking about it but I'm just about to start the 4th world so my take on it is still early. That said, the way I'd describe this game is like an alternate history version of Super Mario 64. SM64 came along and basically set the template of how to do 3D platforming after nothing but 2D adventures and that is what we are all use to. However, after a series of 2D NSMB games, SML3D feels like a 3D version of those games but it is so different from Nintendo's other 3D Mario games. That's why I say it is like this alternate history version of what if Miyamoto wasn't around to have made the 2D - 3D jump and this is what developers may have come up with of how to make that transition. It adds such an interesting layer to this game as I play it.