True, other games do evolve and expand on their core mechanics.
The reason that the galaxy games and now 3D world get so much love is that they don't simply add new powers and that's it, each level has its own uniqueness and they continually suprise moving from one idea to the next. They throw different level ideas at you and discard them just as quickly. That's what makes them fun, the 3D Mario's have become somewhat of a creative explosion of plat forming gameplay. An SM3DW does that at the same time as saluting many of the past Mario games in a way that is just a joy for anyone who grew up on those games. Yes it plays on nostalgia but it does it in a new way so it feels fresh. Add to that this is the first time there has been multiplayer in a 3D mario game. It really does deserve its praise and is definitely not a simple rehash of M64
And like I said, other games do expand and evolve but the 3D Mario's have really developed a something special over the last few installments