The Tanzania coffee character is typical of East African washed (wet-processed) coffees. It is generally bright (acidic), and almost aggressively flavorful. Kenya may still produce more intense coffees, but Tanzania has pushed ahead and shows many of the same positive qualities of Kenya. Coffee is grown in the North and South and there is good quality potential from both areas, although most buyers are more familiar with the northern coffees from around Arusha and Moshi
Peaberries are often sorted out and sold at premiums, but the cup is sometimes tainted and not worth the price. It has become a novelty coffee, and sells well in the US, so many roasters capitulate. Yes, it is a coffee with great potential but shipments arriving in the US do not always express that truly excellent Tanzanian cup. Every so often I cup a really good example of this coffee, but some years are a complete bust. The problem is that Tanzania has realized it gets a premium for its peaberry no matter the quality ... so what's the incentive to actually pick and care for the coffee better, in order to prevent this defective character?
One possibility is the coffee ages (or is steamed essentially) in stalled shipping containers as they wait for a place on the vessel. Dar Es Salaam, as with many tropical port cities, is extraordinarily hot and humid, which can cause rapid deterioration of coffee quality.
Blackburn Estate from Ngorogoro has been a consistently good arrival, the highest rated Tanzania in recent memory. "Northern" coffees are considered to be more "generic", and Kibo has that off, baggy, "steamed in the container" note. The Southern type is a clean cup, zesty, albeit mild next to the Kenyas. Mbinga area has produced a solid cup, and the drier Mbeya region is perfect for coffee processing.
I guess what I'm saying is, there is a definite range of quality coming out of Tanzania, with many top lots suffering damage during transport. So keep in mind that if there is a current Tanzanian offering listed here, not only did it have to overcome many environmental inconsistencies, it also had to overcome my cynicism and must be pretty damn good.