Sales have not been stellar. The hype is not something that rivals a PS3/360 big releases and it has not had any commercials to advertise. I go to my Best Buy and Target the day of the release and neither even knew or had copies of this game out on the floor the day of its release. The staff did not even know that the game came out. These things hurt the potential sales of the game with no public knowledge of its existence. I know this is not true for all regions, but I am going off of what I am seeing firsthand.
Believe it or not, but this can be said of most Nintendo games and a lot of games in general...
- When I bought Super Luigi U on releases, the store I went to had absolutely no clue it even existed.
- When I preordered Pokemon Rumble U, I had not released the game would be releasing the next day.
- A lot of people (my friend included) seemed unaware that Rayman Legends released.
Want to know how bad this got if we want to go off anecdotal evidence?
Back when PlayStation All-Stars Battle Royale first released, I was at BB at opening to get my preordered copy. I got to the back after being burned on Borderlands 2 (another story for another day) and it simply was not on the rack. I was talking to a sales employee, who said he had no clue what that game was. I pointed down to the picture under the plastic thing on the counter, which was an advertisement for the game. He said they never got any in stock, though I told him I found that impossible to believe. The guy got a manager, who said the game wasn't out yet and would be out on blah blah Tuesday. I noted that today was blah blah Tuesday, which instantly changed her tune. She noted that they had copies in stock, but had no clue where they were. This lasted for about half an under before she actually tracked down the game. The stories point? All-Stars was hyped a lot more than The Wonderful 101 was and people still didn't know shit about it.
It can be underrated by the public even if it's beloved by the critics. From what I hear, people weren't beating down doors in Japan to get a copy.
"to rate or value (someone or something) too low"
"the extent to which a product is recognized and bought by customers in a particular market"
This is sort of an on going problem with gamers and really a lot of people on the internet... they instantly jump to a term that makes their point sound better, though that isn't exactly an accurate term. If you want to talk about sales, then say that and not call the game underrated. Most people will read underrated as nothing more than the counter to overrated (something that gets higher / more praise than it deserves) and ultimately leads to confusion. You could have just as easily said under marketed, which is an infinitely more accurate term and one I can't disagree with.