Edited/expanded from another post:
I've only played about 30 turns as England in the Britannia campaign, but here's my initial thoughts:
Billmen put up a fight! I've only seen the Militia variants and not the semi-professional castle-built versions, but they fare better.
Boiling oil is pretty cool, but it's not great against rams. The ram model has been altered a bit and foot units march underneath a covering. I've seen 1 of 3 rams lit ablaze by the oil. Don't expect oil to make rams useless against large settlements like in RTW. However, I wouldn't want a group of my infantry huddled under a gate when the oil comes.
I like the cavalry adjustments. The smaller units take a little getting used to, but they are just as powerful as ever if you hit engaged foot infantry from the flank or rear. Frontal charges against non-spearmen are still strong. I charged a unit of...I forget what now (it was a cheap Welsh foot unit without any cavalry bonuses) and it disappeared underneath my Feudal Knights just like pre-1.03. Cavalry is not nerfed.
Word of warning: spearmen will stop cavalry, even levy spearmen or other low-quality spear units. Combined with small unit sizes, you really have to be mindful of spears when commanding cavalry. Just like it's supposed to be.
Pikes aren't quite the phalanx formation it was in RTW, but I had a unit of mercenary pikemen hold a gate during a city defense and they held formation fairly well (I had pike formation on and defensive stance). They were crushed because William Wallace personally attacked the settlement and 100 guys with pikes can't stand against 1000 guys with swords, but they did way better than I expected. I still haven't seen cavarly charge into a pike wall, but I expect the pikes to win that battle.
Archers seem to work about the same as before, although weaker units (archer militia for example) seem to be a little less effective. Their best use is the moral damage of flaming arrows, because they won't do a lot of extra damage if the enemy has shields or armor. Then again, regular unupgraded Longbows vs. guys without armor or shields are very effective.
Campaign events are cool. I can't speak for the others, but in this campaign gunpowder happens early (around turn 30?). Also, my faction leader Edward was invited to go on a Crusade and I accepted, so now he's off the map somewhere hopefully not getting killed. If he comes back, supposedly he'll be very powerful. There are other things but I won't spoil them...
The music is very good. It sets the mood well and I'm very pleased with the work they've done in the music department. The expansion doesn't come with a music CD but you can unpack the music file and get all of it anyway.
No, I'm not being sarcastic.
[This message has been edited by Smileyman007 (edited 08-31-2007 @ 03:17 PM).]