For me RY4 (Dekang) tastes like carmel and vanilla. However, I have tried several different RY4 recipes and no two are the same. Joye is harsher, more tobacco flavor, Dekang is fairly sweet, and some of the US made is VERY sweet.
My "main" vape is 2 drops chocolate with 1 drop of cappucino. I mix it up in a 10ml bottle and add 12 drops of vanilla when I reach the top. (So ~1/8 of a drop of vanilla.)
However, I also switch in the RY4 on occasion. I find if I keep vaping the same flavor all day, I stop tasting it. Much like I never really "tasted" a Camel Filter until I smoked someone else's cigs and noticed the difference.
For a robust tobacco flavor, I like French Pipe. (I switched to smoking a pipe a few years ago) My pipe tobacco was usually a Vanilla-Raspberry blend. So I take french pipe and add some vanilla and blackberry/blueberry flavor to it. Nice after a heavily flavored dinner. (Who can still taste RY4 after a nice goat curry?)
RY4 also makes a very nice "base" to add other flavors to. Some of the fruit flavors taste manky to me at full strength, so I mix them half-and-half with RY4.
IMHO, RY4 is an idea now... A tobacco flavor with carmel and vanilla. The actual execution of that idea is different for every juice maker. Your taste buds may vary, but when you read RY4, the maker is shooting for a tobacco flavor with carmel and vanilla.