I played M&B a bunch when it was in beta, and went through the tedious business of conquering the entire realm once after it was finally released. It's been a few years and I was itching to play again, so I picked up Warband. It is cool, but not too different from vanilla so I added Floris to it.
Most of what I wanted out of the mod was an expansion on trade and diplomacy and such. I wanted to try my hand at being a merchant, and did not want to play in a historical setting or someone's home-brew fantasy setting, or something based on a series of popular books or something. It was a toss-up between Native Expansion and Floris, and it seemed like Floris had better economic features and such.
I have to say though, Floris suffers from the typical "kitchen sink" style of modding. I've got a core i7 3rd gen with a GTX660M 2GB, and there are still occasionally problems with textures because of how damn many are thrown in. The interface modifications like the in-game troop trees are always glitching.
By and large, it runs pretty well. but there are a few problems here and there.
Most of what irks me though, is that even though trade and economics are expanded it is still difficult to play as a trader. I feel like it was easier to make a profit buying and selling goods in vanilla.
Also, I'm not a fan of the new NPCs. The writing in the original game was pretty high quality, and referenced a somewhat consistent larger world. Now we have all these NPCs talking about the real europe, and all sorts of church references and religious icons and NPCs that were not a part of the game before. it just feels totally different.
After a couple of trys, I found myself going back to vanilla Warband. I'll probably give it another shot sometime, there is a bunch of cool stuff there. I hear there is still one more version yet to be released, so maybe it will improve a little bit?