Having fun with a really tough game as Isabella on Emperess. I decided to play a spiritual leader to get to know the civic table a little better.
It's ages ago that I played unmodded BTS last, so it's diffucult to see what's going on and going wrong for me in late medieval, early renaissance times. At this stage, the AI is teching horrendously fast, even taking in account the AI is playing on Noble. I looked into the CIV4HandicapInfo.xml and found not much of a difference to BTS. iResearch is set to 130, was 120. And the AI starts with four initial techs, was two. I rule these factors out, because in the ancient era I was on par or ahead. Has anyone encountered this phenomenon? Otherwise it must be my sleepy playing and being used to a mod that's restricted to antiquity.
Since the unlimited specialists were removed from Caste System, you are bound to build cottages to generate commerce for research – once you eventually researched Employment. You will have to wait then for Democracy to run unlimited scientists. This amounts with the now missing three beakers per specialist through Representation to a drastic dependency on the base commerce of your starting position, regarding your research speed. And there's not much to decide, to try, to risk, to do something about that initial commerce situation by your own choice, mostly because you can't snatch Representation anymore by chopping the Pyramids (free choice of government civics) very early! I do like the change to Caste System and Pyramids, but where the hell are the early beakers are supposed to come from, now

?
I was lucky to have a productive starting location with horses next to the capital. I killed my next neighbour right away and his capital was excellent; that's why I stayed on par for a long time. In my first two games, I was doing very bad, though, and this aggressive approach and exploiting the building of wealth as soon as possible appears the only viable solution.
My second next neighbour was Protective. Driving me nuts with the Medic promotion. The meaning of being a protective leader turns into the opposite, if Medic promoted chariots are perfectly well suited for early rushes, really inviting you to raid the enemies instead of protecting your frontiers from raiding enemies. I wish I had had them.
Mapscripts:
When I tried the World mapscript, all settings medium and normal, culturally linked, old word start, it returned a strange Standard size map that left space to claim 25 cities for each civ without conflict, even though I added more starting civs than default, expecting some immediate fighting about settlement locations. And it returned the civs starting everywhere.
Tectonics is giving me all kinds of strange Tundra starts, and the maps look arid altogether, despite I selected temperate.
I hope I'm not putting you on the wrong track, Xyth, but in my impression, there's something buggy with those map scripts – perhaps connected to the "culturally linked Python

.
Bugs:
The Olympic bug is still in, held games won't leave cities, sometimes.
I remember my warrior pillaged, civic was Militia. In Vassalage and Conscription pillaging is impossible.
Miscellaneous:
Post office, custom house and tavern seem too close techwise, although they may fit there thematically. No big problem, but you're queuing several alike buildings in your cities.
I like the cuneiform loading screen very much, starting to understand my first words while the game is loading

, but in one of the info screens, it makes for a hard read.