Great game, sometimes amazing, sometimes so frustratingly painful...
Pros:
I haven't played a Mario side-scroller since Super Mario World 2, so this was very nostalgic to play. Pretty much the same controller layout as the originals from way back when.
The world map layout was similar to the good old days, except for a few tweaks. I liked how you had to defeat certain bosses in a certain manner to unlock other worlds.
The cannons were a nice touch. Reminds me of the pipes to certain worlds from the old NES games. Except you didn't know where the cannon was sending you until it fired!
I didn't have to use the stylus at all, all you have to do is use your right thumb on the screen.
I liked the new power-ups (Giant Mario, Mini Mario, Turtle Mario)
The mini-games were a nice touch, a la Mario Party.
Cons:
Very difficult to save on the first play through. Makes the game really frustrating at the start. You pretty much have to run to the end and beat the game before you can go back and unlock everything.
No Tanooki suit? Come on, I was so waiting to put that on again!
Certain star coins required certain power-ups that weren't on the level, making the game sometimes frustrating.
There was an absurd number of 1-ups in this game. Toad had way too many green houses in this game. By the end, I had 90+ lives.
Overall:
I found the game to be enjoyable overall. The one thing that ticked me off about the game was that to get certain star coins, you needed a mini-mushroom or turtle shell. Now if the power-up is in the level, that's cool. When it's not, it becomes annoying to visit toad's houses to pick one up by timing the box right OR having to backtrack to a previous level so you can store the power-up and use it later. I wasted a couple hours trying to get the star coins that required Mini-Mario which really took away from the game.