Galaxy has a lot more charm, the galaxy scope of it even if it is linear just adds a lot to it. You actually feel you're in space with the rounded planets, the anti gravity levels and launching into space every now and then. I never got bored of that. The music was simply amazing and it doesn't give you the impression that you're going from one map to the other.
Thing is video games evolve, and while I like my dose of 2D Mario, I don't want to see any of the restrictive 2D design levels in a 3D Mario game. Galaxy, as linear as it may be, was far from a 2.5D game. Even 2D games have stuff to explore but limiting your run to a set time on each level and having to get to a "meaningless" pole (it's a 2D level design really) instead of getting the star just makes the game seem caged, like it's locked itself in a constricted world.
I liked 3D World but I always had that feeling of playing a 2D game and I could never shake it off. Whereas in Galaxy Mario seemed free, and there's nothing more free than space.
One more thing is that I truly believe that 2D Mario is for the fans of 2D Mario platformers where they are rehashed for older fans where as 3D Mario was always kind of a risky venture for Nintendo. SM64 was the first 3D Mario game and they had to get out of their comfort zone to make it, Sunshine was a big risk in the direction for the Mario series, Galaxy was just going out of the conventional castle design into space where as 3D World seemed more like a fleshed out 2D Mario, and tbh I like Nintendo the most when they take risks.
And btw to anyone dissing the Wii controls in the game, bar the racing games I thought it was implemented beautifully and one of the reasons I feel in love with the game.
