It hasn't got any more variety in environment than NSMB does, but I'd argue that the sprites have more charm than the (first three) NSMB games do.
ha come on, i didn't want to go in that war again but let's go, i'll try.. cause it's pretty hard to explain after all.
Take that from Mario world.
it's, indeed, not varied at all and repetitive in the patterns. BUT,weirdly, it works. Cause the art direction is strong and the minimalistic style + color palette makes it just natural as it is.
Where in some of that screens, particularly the one with the big geometric mountain behind, it just looks like a messy copy and paste all over the place!
Big difference is that Mario World doesn't try to be realistic or detailed. It's iconic and symbolic, maybe even abstract and design, and it's perfectly handled. Now NMB is more detailed and in the same time less natural. Everything is at its right place in Mario World, when things look random and messy in NMB.