I wrote some impressions
here. In Spanish.
Basically it's what I expected.
A game with soul, that goes right to the point despite Professor's speeches :lol.
I've felt like my-15-year-old-self, that played for hours and hours with Luigi's Mansion in GC.
This is a kind of game that feels and plays from the days when you just put the cartridge in your console and pressed start.
Technically looks way better than screenshots and videos. I highly recomend to play it before judging if it looks bad, like some people have assumed. It's not the first game in 3DS that looks better when you actually play it than when you watch videos.
Gameplay is exactly the same as the first LM but lacking the second stick, which I haven't missed so far. The Gyro controls are fine, but aren't strictly necessary. You just can capture ghosts by placing yourself in front of them.
But, imo, the best feature in the game is the sound. The music and sound effects are so well placed. Even you can use the d-pad to make Luigi speak "Hello~~.." Lovely.
Another word that defines the game is charm. Everything is charming: Luigi, Polterpup, the ghosts, E. Gadd, the settings, the mansions...
I was able to play one multiplayer game with some japanese guys. I dunno if too many people will play this but I can assure you it was fun as hell, despite we lost during the third mission because we didn't worked on co-op. Don't be greedy, that's the point of multiplayer.