This is a really good game.
It’s interesting, having played Super Mario World before this, to see how much Mario World borrows from Mario Bros. 3. Enemies especially appear to have originated in Mario Bros. 3 and been used in subsequent Mario games. Dry Bones, Thwomp, Bullet Bill, and the Koopa Bros, to name a few.
The difficulty level is a bit higher than in Mario World. It was never unbearable though.
I recommend this. It’s among the best side-scrolling platformers I’ve played.