Is it just me or is the interface of this game really, really bad ?
It might be just you. The UI/UX of this game is light-years beyond most any game or app I've encountered. Very well thought out in many respects, and having increased functionality for those you happen upon it or try it. Once you play it a while, it makes more sense and you come across cool nuances and extra capabilities for power users.
Has some shortcomings, sure. But I'm amazed how much you can do and wish more app and game makers paid more attention to the details Larian has.
I also personally enjoy meticulous, intricate, detailed UIs, so this one is down my alley. I love that you need to click the precise pixels, and very rarely mis-clicked. That was not an issue for me at all, except maybe early early on when I was getting used to the game, or the doorways in a couple battles.
I hate UIs that have big, bubbly icons everywhere, a ton of vertical/horizontal padding around text or buttons, big fonts, and the like. Generally, I dislike interfaces designed for users with 13" monitors or those who want a more casual, mobile phone-like experience... with some Metro-style interface where all the buttons are devoid of color (or all the same color) and generic/basic 2-D line art representations of everything just to look kewl and modern to follow graphic design trends of the past decade.