Lots of questions!
Well, it's almost the same as the Wii and DS game. If you like it to be different, it's not for you.
I have it and I love it. If you have the chance you might want to try a demo (if available) before buying.
You'll gather lots of coins even when you ignore them. :P When you gather 1 million coins the start screen changes. Apart from that there's not much purpose to them.
I like it about the same as the other 2 games.
Difficulty level is subjective... I found it to be very easy. I beat Bowser after less than 4 hours. It gets a bit more challenging if you want all Star coins and Moon coins (In the special Star World you collect Moon coins instead of Star coins. :P)
Turtle shells cannot be kicked upwards. :/
Hope this helps.
You can also read some impressions here:
http://gamrconnect.vgchartz.com/thread.php?id=146017
and here:
http://gamrconnect.vgchartz.com/thread.php?id=145815
Need something off Play-Asia? http://www.play-asia.com/
