I've noticed that Light Infantry have a weird glitch in their combat animation where one of the guns is pointing straight up while the soldier acts like he's firing it at the enemy.
That's just some good ol' YEEHAW!
Does any of the factors I implied actualy affect the tech transfer or should I just increase difficulty ?
Tech transfer is at a set rate. You receive a reduction in research cost for the first civ you have open borders with who has discovered that tech. Any additional open borders with another civ after that will also reduce the research cost, but at a lower rate.
Increasing the difficulty will have the biggest effect on the research gap between you and the AI, however it will not effect tech transfer. What it will do is give the AI an advantage by allowing them to generate more beakers from their cities than you can.
About the levies : on legendary speed production difference between the irregulars and fusiliers are 1-2 turns and it doesn't compensate the power gap at all :< I would consider reducing their cost even more , does anyone agree with that ?
I agree. I never build irregular units for this reason unless I don't have the proper resources. If they were cheaper I would build them if I needed to defend, or launch a counter attack very quickly.
In my Aztec game All eastern factions exept for the Mongols, Dravidian empire and Japan(duo to isolation) got crushed by the barbarians pretty easily. What is your experience on that matter guyz?
Japan usually survives, but is relatively weak. The Chinas, Korea, and the Khmers generally have a pretty rough go. I don't play as either of those on the world maps. IMO, they are the hardest civs to play as in that scenario, due to the relentless insanely large hordes of barbarians. Also on a lot of games the Mongols get pretty scary and if you haven't had a chance to build up (due to relentless barbarian attacks) they will steamroll you.
P.S. Also, in the same game English empire went "wonder whoring"(no Great Libraby-Gondenashpur combo though
) and doubles my gold income with their 4 cities and soon will be ahead of me in techs by almost an era(wooho... Long live the Queen).
Elizabeth is the biggest wonder whore this game has ever seen! England wonder whores every game I play usually, however it works out ok with their bad starting location that doesn't allow them to expand until after the New World is discovered. Elizabeth's wonder whoring simply allows her to keep on par, or remain slightly ahead of everyone tech wise until that point.
After the New World is discovered England usually is a big threat if you let them conquer most of NA. Before that point, you don't even need a navy as long as you have a coastal city in north western France so you can easily invade them. If you don't England is no threat as long as you have a good navy.
I always get annoyed when they build the Pyramids in London... it just doesn't fit. I find it funny that Egypt usually never build the Pyramids, or the Spinx, but has an excellent starting location with all that stone and awesome food and production tiles.
. In renesance, so it looks like I will not see that industrial age again 
. I would like to have some 1st, 2nd world war like games 
