After reading Bhawb's report above, I tried out Timur with an aggressive Authority early-rush gameplay. The result was pretty neat. (Setting: immortal, standard, communitas, with other mods including 3/4UC, Enginseer's Civic and Reform, Bare Necessity and a bunch of other UI improvements)
I started on a continent with five other AIs. The continent was divided like a three leaf clover, with Austria and I on one corner, Babylon and Songhai the second, and Byzantium and Greece the third. My start was alright - not many food in capital due to tundra start, but I got the 6-faith mountain wonder nearby, so that allowed me to found a religion. After researching pottery to build a second city grabbing the 6-faith wonder, I researched iron working and immediately rushed Austria. I was quite fortunate to be able to capture an unguarded Salzburg within two turns (I razed it and built Merv directly on top of its former site). The yields from the UA is fantastic: you get four of almost every yields from capturing and razing a city (to put it into perspective, Morocco's UA only gives you one of everything), which really helped me with the city development and catching up with culture, science and founding religion when you only have ~5 culture or ~10 science. Kudos to pineappledan for increasing the yields from UA: now I can definitely feel its impact.
Austria offered little resistance afterwards, so after capturing Vienna, I captured a city state next to Songhai's border as an invasion point. This is where I encountered the greatest difficulty: even though Songhai's technologically lagging behind due to a lost war with Babylon, his UA, combined with the river-heavy Communitas map really made him a terrifying opponent. I actually had to restart once because I was not aggressive enough and let him tech to chivalry to get his too UUs (in 4UC mandekaly cavalry is moved to chivalry). But between a citadel and my powerhouse capital, I was manage to vassalize him before he reaches medieval era.
Afterwards, since Greece has settled onto my third of continent and got DoW'ed by Byzantium, I DoW'ed on him too and captured two cities (razed one and puppeted another), and by beelining chemistry, my tumehy marched to his cities, who offered little resistance since apparently he has no mobile units and did not research military techs. Now I am marching to the Holy City of Athens with the nice Great Lighthouse.
My religion includes the tundra pantheon, Hero Worship, Orders (for more faith), Mosque, Iconography and Crusader Spirit, so I can pursue a heavy GA-focused strategy to give me a lead in culture and economy.
Now concerning the power of the UA, my capital is allowed to develop to something almost like a tradition capital. I captured/razed around 10 cities in total, so that's about 40 yields of everything in renaissance. This is massive: in my capital, my palace alone contributed to around one-fifth of my production, one-fourth of my culture, and one-third of my science. I guess this also gave me many surplus happiness in my capital, allowing it to grow really large, and to wonder-whore a bit.
As for the buildings from captured cities, here's what I get in chronological order: market (Salzburg), library (Vienna), water mill (Gao), writer's guild and chancery (Corinth). Pretty decent, I guess. They do allow my capital to build wonders and military units and ignore some infrastructure buildings for a while, since you can use the yields from UA to compensate.
Overall, the gameplay reminds me a bit of France or Assyria - a tall-ish warmonger with not many direct bonus to fighting but great bonus from fighting, but unstoppable once it gets the gear running. I'll argue that you need authority to utilize the great yields from your UA.