True to the series
So the first question is: what's old? New SMB embraces the new Nintendo focus of simplicity. It uses the D-pad and 2 of the 4 buttons - and that's it. This game could be played with an NES controller. The touch screen components are minimal and could easily be taken out without affecting the game. It has the core gameplay of the original SMB. Tack on the overworld aspect of SMB3. Then sprinkle in the secret exits, alternate paths, and special coin collecting of SMW.
Oh, the "New"? New moves: wall jump and butt stomp. Both are used liberally to access secrets and coins. New power-ups: huge mushroom, mini mushroom, and blue koopa shell. The mini mushroom in particular is utilized for special areas. There's some strategy required with these new power ups, as you rarely find them in the levels themselves...
The environments are typically Mario, and the graphics are beautiful, some of the best 2D graphics ever. The challenge level is significant if you like finding all the secrets, but not too bad if you just like blowing through levels. The music is quite cool, catchy remixes of tunes from all the previous games.
There are a few things that can be annoying. First, you can only save after completing a tower or castle level, or after spending coins to access a blocked path. This is really weird, and frustrating if you just want to blow through a level on the bus - you can't save anywhere. The control underwater is real floaty, making these levels even more of a pain then the original game.
Highly recommended, and a worthy addition to the pantheon of 2D Mario classics!