"Great" in my mind is getting up there with the elite that is just too small of a sampling to discuss in the "unassuming" category. The consensus greats (regardless of how they come in on your order of top 10 or to 50, whatever) are all pretty much known, and accepted to varying degrees. They may be controversial in terms of if X id greater than Y, but they are all highly recognised for their playing greatness.
At least in my thought of what is unassuming, I have to first think of understated, or unheralded, or even hidden gem sort of concept. To that end, I think there are quite a few (even if this smallish 1500 group seems to know them well) The Rustic Canyons, Wild Horses, Apache Strongholds, (and I hope soon Port Lavacca's) seem to be more in that unassuming, very good category. There are dozens if not 100s of those very good unassuming ones, in my view.