Looking at the power rankings made by other users, Ethiopia doesn't seem to get the love it deserves. JungleBucks (Dec 2) rates 23 civ's over Ethiopia and 14 below it. Dawnbringer (Oct 31) considers 18 civs better than Ethiopia and 18 worse than it. On Enrico Swagolo's most recent list (Oct 18), 23 are placed above Ethiopia and 12 below it. The overall impression on Ethiopia seems to be that it's a (lower) mid tier civ. I, however, strongly disagree with that statement. For me, Ethiopia is and for a long time has been a top tier civ and I can only come up with 2 or 3 civ's that could be considered better than it.
Stele is (one of) the strongest unique buildings in the game. With any other civ, you must make a decision between early shrine and early monument. The former increases your odds to religion and a solid pantheon significantly and the latter doubles your culture, which is a yield that has a strong tendency to snowball. With Ethiopia, you don't need to make this decision, since stele gives you the faith of shrine and more culture than monument. You are basically guaranteed to get a religion early since you have 2 buildings that give you faith.
The importance of the free techs from UA seems to be underrated. If your aiming for science victory, their importance should be obvious. If you're looking for any other victory, they also serve a purpose. You can focus more heavily on your preferred victory type and, to some extent, neglect science as a yield and still remain as one of the most literate civs. The synergy between the free techs and cultural victory is particularly good, since you should be getting lots of culture anyway and science is often the limiting factor that prevents you from building a world wonder. This happens particularly on reneissance, where you have great wonders like Uffizi and Leaning tower of Pisa on both sides of the tech tree.
Overall, the combination of Ethiopia's UA and UB is amazing. They help you considerably on early to mid game culture and science, which helps you securing the key wonders and allows you to snowball to victory. Mehal sefari is something I don't have personal experience with mainly because I only remember finishing one game on Ethiopia and I won a cultural victory around the time I opened rifling. Late unlock is obviously the worst part of the UU and I personally dislike units with combat bonus on owned lands, as you don't want to be fighting there in the first place. On the other hand, the importance of a UU is significantly smaller than that of UA and UB and this is particularly true on more peaceful and passive civs like Ethiopia.
Usually, I have chosen tradition as my opening policy tree with Ethiopia and focused on a strong capital and specialist. Since I nowadays consider tradition a bit lacking and authority OP, I decided to try authority Ethiopia. As always, I chose immortal difficulty, continents map type, standard game speed and standard map size. I ended up enhancing my religion before anyone else had founded thiers, having 22 techs (Education from medieval and all classical techs except metal casting) on turn 89 and 8 policies on turn 98. There is no other civ that can do all this. I didn't even neglect my army. It wasn't massive but big enough to defend my lands. I was quite surprised to notice that it was the biggest in the world, since usually AIs would have more units by that time of the game.