Feel free to recommend what you would like to see
Since your interested in what people would like to see in a custom made world, the main thing I look for is lot sizes. I have no use for a world thats filled with custom sized lots because that means I'll most likely have to build my own houses rather than have the option to download houses among the many thousands upon thousands of really nice ready to download and install homes.
And, what I consider custom size lots are sizes such as 21x31, 41x65, 18x12, 32x75, basically sizes that are not standard. What I consider standard lot sizes are sizes that you'd find in Sunset Valley or Riverview such as 20x30, 30x30, 40x30, 40x40, 60x60. So, since 99% of the homes available for download are made for standard lots, and so many of them are really well made, why veer off that path and fill a world with lot sizes that you can't use. Unless of course you'd rather fill your world with houses you built yourself but i've been in this community long enough to know that probably the majority of people would rather download houses than build them. And filling a world with custom size lots is all well and fine if you indeed build all your own houses, but if your intention is to share your world, please consider that lots of people might want the option to just download a bunch of houses and fill your world with them.
I've downloaded alot of worlds that looked great but were filled with lots of custom size lots. I look around the new worlds and wonder what people have against 60x60 lots. Needless to say, not one world has passed my personal test yet so, all those worlds got deleted from my game. Speaking for myself, as much as I'm ready for a change from Sunset Valley and Riverview, I haven't found a world yet that I want to play.