New Super Mario Bros. 2

[NICKtendo DS]

Good graphics and sound make a game attractive.
Good gameplay makes a game fun.

A game with horrible graphics may be fun to play, but unattractive, which means people are less likely to play it.
A game with horrible gameplay, but great graphics is more likely to be played, but makes the buyer regret his/her purchase, which might lead to poor sales of the same series in the future or overall cancellation.

Graphics and gameplay are both important. Looking at NSMB2, the graphics are bland and repetitive, which influences the experience. Nonetheless, the graphics are not horrible and the gameplay may balance it out. To be honest, SM3DL was a let down for me, because it was more 'I have to' than 'I want to', ruining valuable replayability and for a 3D Mario game not to have alternative paths, not even on the friggin maps!, it's a bloody shame. The whole 3D with 2D gameplay was mere sugarcoating for something that'll rot in the shelf once you're finally done.
I did replay NSMBDS from time to time. Destroying the flagpole at the end of 1-1 hardly gets old. I suspect that despite the same old exterior, it's going to be enjoyable. It's going to be 'I want to'.