>>2750190It suffers from being sandwiched between two of the greatest games of all time, making it look lackluster by comparison, even though it's still a great game in its own right.
Mario 3 had more unique presentation, superior level design, more variety, better balance, and it was just simply deeper and more memorable. A feather that gives Mario a cape is simply not as compelling as a leaf which turns him into a racoon.
It introduced Yoshi, which was cool, but he was underdeveloped in terms of usefulness and abilities. He didn't really shine until Yoshi's Island, another game which trumps SMW in terms of presentation, level design, and depth. The mechanics of SMW are completely bare-bones next to those of Yoshi's Island.
The only things World has got going for it over its predecessor and successor are the overworld, with its cohesive structure and branching paths, as well as the novelty of the two secret worlds. Finding a secret world inside the secret world was mind-blowing the first time you did it. Mario 3 had a stylish map, but it was a bit shallow next to that of SMW. Yoshi's Island didn't even try to make a fleshed out overworld.
SMW is still a great game though.