Formations, could do without, though should perhaps be optional. For those of us who wish to play this strategically then it would be a nice addition, but for those who just want pure, unadulterated carnage of a charge, then let it be turned off. Not sure if this is possible to have formations optional, but if so then I would suggest it.
Shield bashing, cool to see and also useful. Perhaps you're dueling a lord or king and they get the upper hand, you could shield bash to regain your breath, but so could he do so to you, and I have experienced a swarm of shield bashing when I attacked a castle. Mostly just used when swarmed and using hit-and-run tactics.
I would however like to see if spear bracing could be added. I personally find any horseback fighting to be imba. One possible counter to cavalry charges is ranged warfare and have only succeeded in quelling a cavalry charge with archers is when I had about 50 again 10 as AI archers just shoot in the general direction and I find they hardly hit anything. The other option would be to slash and attempt to dodge the enemy charge, though you can stop the cav when in tight formation, it usually is broken after the first attack, and you'd then have to result to slash and dodge unless you're able to swarm. Spear bracing makes the character think twice before charging in with a horse against spearmen and makes it a bit easier to handle cavalry if using a spear.
Just my thoughts, apologies if it was too long for just a few features.