Finished a really long game (Marathon, Pangaea, 22 civs, huge, King) with Assyria. Some thoughts:
The conquering part of the UA has a bit of a stepping stone to it (took me a few tries to get the early game right), but scales very, very nicely - once you get to the part where you finish Tradition and start aggressively looking for people to mess with, those science jumps really help make you lead in science... or get away further. Combined with the other part of the UA, snowballing away with science is very fun and possible, particularly in combination with the recent 'puppets no more increasing science cost' change. Being ahead in science is almost a necessity too, as in a Pangaea everyone hates you for your warmongering by midgame and you're in constant war. But really, what's -145 happiness when you're about to own the world? (As a sidenote, learned the hard way that warmongering penalty for repeatedly killing off someone is pretty big. People really, really did not like me after I killed Askia, someone else liberated them, then I killed them off again - repeated a few times.)
Siege Tower does its' job fine(notably, helping get that early city siege going without having to protect cumbersome and weak catapults), although adding Medic 2 probably would not hurt. I'd say keep them and Great Generals separate though.
This game was started before the recent Royal Library change, and the prebuilt piece of tablet + extra slot in there probably does help with what I'd ask for anyway - being able to 'fill' it at a reasonable pace. That said, post Military Academy four promotions is borderline ludicrous. March/Logistics right off the bat is crazy good, no doubt about that.
Flavorwise... yeah, I sort of agree that Assyria should maybe be more about conquering before most people have discovered how to read and getting ahead that way, buuut I don't really have problems with the current set of uniques either.