I feel have become intimately acquainted to an uncomfortable degree with various aggravations that the time has come for me to itemize the sources of my aggravations. My impression of the UI in its current state is that it was designed for aesthetics first, functionality fourth. I am loving this game but there is much, much room for me to love it even more. Here is a list of things I would very much like to see improved in future patches.
The lack of a bow reticle is only just scratching the surface. Enough has been said about this by other people and there is a very simple mod to fix it so I will refrain from adding my two thousand cents, but I still support the addition of a Settings option for this feature.
The inability to reference alchemy recipes at any time other than when I am operating the alchemy bench is a huge frustration. I have to either look at screenshots of the recipes or else have a webpage open at all times while I am doing alchemy so I can know what ingredients to transfer from my storage trunk to my inventory before I venture off to a bench. Either way, I have to look outside of the game in order to take a necessary action within the game. That’s immersion taboo 101.
Workflows during NPC interaction are the worst. For starters, the lack of an indicator of my reputation with a given vendor during haggling is just stupid. The only place where this rep stat is visible is during the trade screen, but not during haggling and not during repairs. So if I want to know how far I can push an NPC’s patience on the first haggle bid, even if I’m visiting him only for repairs, I first need to open a trade negotiation and memorize whatever number appears at the top of my screen, then exit and begin the repair negotiation.
Another workflow issue is the habit of the game to kick me out of interaction with an NPC once I have completed, or failed to engage, a given monetary exchange, such as the aforementioned switch from trade to repair dialogues. If I want to do further business, I need to once again interact and ensnare that NPC into conversation.
One of the most keenly aggravating workflow hindrances despite its rarity of use is that of not being able to auto-divide my inventory resource stacks when transferring to my horse. If transferring the full stack would exceed my horse’s carrying capacity, the game simply tells me so and cancels the attempt wholesale. Not fun when I am trying to loot during combat before the corpse becomes lost in the undergrowth or chase down an additional boar/deer that was in sight just moments ago. I would much rather see the game do the math itself and auto-divide the stack so that whatever the horse can carry is transferred while the remainder remains in my own inventory. Every other RPG I have ever played that involves such transactions does this; why not KCD?!?!?!
While we’re on the subject of the horse… If you’re like me and you use your horse like a pack mule with an inventory that would shame a traveling salesman, I expect you can relate to this desire. I would love to see the horse’s inventory come with collapsible/expandable category sections where each collapse/expanse is persistent until I click on it again. Enough said.
The final workflow problem for this list is the seemingly tiny issue of the Player tab being in between the Inventory tab and the Horse tab. Seems like a little thing. But I can not even begin to tell you how many times I have mistakenly clicked on that Player tab when trying to alternate between my Inventory and my Horse (aka my second Inventory) simply because that Player tab was situated in between the two. If the Player tab was on the left end of that menu window, with the Inventory tab occupying the second position adjacent to the third tab of Horse, then that would solve a countless number of misclicks and side-by-side inventory comparisons.
Thank you, Warhorse, for making a great game. Now please make it greater. 
EDIT The following paragraph can be ignored. I failed to notice, in the 100 hours I had played up until creating this post, that the Nourishment stat was in the right side of the Inventory screen the entire time. My bad.
Yet another workflow constraint is the lack of an on-screen reference for my current Nourishment level when I am attempting to eat something I am carrying. The one and only purpose for eating is to replenish my Nourishment stat, yet the only two places where I can see that Nourishment stat are if I go into my Player tab – versus my Inventory tab, where the food is 95% of the time – or if I pass time, whether that passage be by waiting, sleeping, or quick travel. Nowhere, NOWHERE in my Inventory screen is my Nourishment level displayed. It’s just extra clicks that shouldn’t be necessary.