Effort is now solely based around art direction and audio design. Of course, the "easy" stuff is just that pesky level design.
I never said anything about it only being art and audio. That does factor in to effort, but so do a ton of other things that the New Mario games are skimping on. Like general creativity, boss design, basic plot and map design.
Honestly, at this point people should expect innovation with the 3D side of Mario platformers. With classic Mario, it would be unwise to change the formula drastically.
Originality has helped 2D Mario more than it hurt, though. SMB2 (US version), SMB3, SMW, Yoshi's Island, and NSMB all had significantly different gameplay designs from the last game. NSMBW was like NSMB, but it made noticeable improvements in difficulty, exploration, and variety. MOST of those were well-received as top tier games.
NSMB2 is the first to both not have an original design and not improve on the design it's inheriting in some way.
Instead it's a weaker version of NSMBW with less interesting bosses, less power-ups, and a **** load of coins (but still not nearly enough to hit the million-coin milestones without having to grind).