You won't find THE answer to your questions - preferences are as divers as there are players out there. The most important thing is that you enjoy what you do, and share if you feel like it. That the number of recommendations/likes/thanks never matches the number of downloads is common on all sites, so don't worry about it too much. I skimmed through some of your world threads here and you got nice comments there. That's worth a lot.
Reasons for me to recommend worlds:
For me, seeing a world "grow", seeing how the creator puts thought and effort into it, having lots of screenshots of different areas, different times of the day, different seasons is already the first step to a recommendation. You know, a bit like window shopping.
Another aspect is if I find a world is well done and well tested. Routing works, no lot glitches, no stuck sims (i.e. not more than the usual EA routing failures). All required information given. Scenic views, a bit variation in terrain and vegetation without falling into the "all on one map" trap. A good amount of objects/decorations, not too many as not to cause lag. Good lighting. Detail.
A world has a good theme - you can plop right into a vacation gameplay, a historic gameplay, a Midnight Sun challenge, a legacy.
So overall a world to recommend in my eyes stands out a bit, is interesting, is one you can identify just by looking at the screenshots.
Reasons for me not to recommend worlds:
Lack of detail. Not necessarily as in number of decor objects on lot, but in general. Was the terrain painting done with autopaint? Is it mainly standard green, some mountains with that horribly tiling rock texture and a flat beach all done with the 4 default terrain textures and maybe a few extras? Boring. Not to recommend. What is the theme of the world? Is it just a different layout for the always same (usually North American) box-like looking houses, a hint of Victorian style, EA rabbitholes? Also nothing I would recommend. There are so many of these worlds out there, and they seem all very interchangeable.
It doesn't have much to do with the use of CC. Good worlds can or cannot use CC.
