The speed is really fast, imo. I watched my son play vanilla M2TW yesterday and stuff died SO much slower in that. You could actually zoom in and watch the cool animations. In STW, I pretty much just see sprites - I don't get to see the models of my men.

It's not so fast that you can't control the battle (though heaven help you if you refuse to pause). However, things do happen so fast you can easily lose a unit of cavalry on one part of the battle if you micromanage the other. You just have to pause often and you can be as tactical as you like.

The upside is that battles are fast now and you will be fighting A LOT to become Shogun, so at a strategic level the game feels better paced than M2TW. The turns seem to go faster.

If I could mod the game to slow it down, EB and RTR style, I definitely would. This would be for aesthetic reasons more than gameplay reasons though. There are mini-mods for slower movement speed, but these would boost archery which is already uber, so you'd need to mod that. Nothing much to just slow down kill rates in melee yet, aside from mods that change other stuff - which I am always reluctant to do. I want to master the game out of the box, then I will look at overhaul mods.

Bottomline - speed is an issue, but the game improves so significantly over M2TW and RTW that I would not let it deter you. The AI, in particular, is so much better. It feels like STW or MTW AI with RTW/M2TW graphics and map.