As a new player, I feel the user interface is somewhat clunky. I'd like to offer the following suggestions:
1. The "E" key is too easy to press by mistake. All the keys surrounding "E" change the view. They are pressed when the player is looking at the screen, yet they require a floating hand position (i.e. a position that can't be found by feel, such as the default typing position which uses the bumps on "F" and "J"). Given this situation, "E" is probably the single most likely key on the entire keyboard to be pressed by mistake. Therefore I recommend that the End Turn key be changed to something else. (I know the key bindings can be reconfigured by the user, but I'm suggesting a change to the defaults.)
2. The left mouse button sometimes shoots, sometimes moves, and sometimes changes the selected squad member. The developers have done a good job providing visual cues about which action will happen. Nevertheless, I have accidentally moved squad members when I really meant to change the selection, and I have accidentally instructed squad members to shoot other squad members when I really meant to change the selection. The game has an option to confirm movement, and I find that option does a great job of preventing accidental movement; I recommend that the developers make that option the default. Furthermore, I suggest they create a similar option to help prevent squad members from targeting each other (or, better yet, simply make such targeting impossible).
3. The right mouse button sometimes backs out of the current command and sometimes changes the orientation of the squad member. It is too easy for the player to change orientation (and spend TUs) accidentally when they really intend just to cancel out of a pending command. I suggest the developers either stop using right-click to cancel or stop using right-click to change orientation. My preference would be for shift-right-click, not right-click, to change orientation.
4. When a button opens a window, that same button should close the window. I'm thinking specifically about the Physical Stats and Inventory buttons in combat mode, but there are other places where this rule applies as well.
5. It would be nice if the keys for changing the view in combat mode also worked in geoscape mode.
Experienced users are probably proficient with the existing controls and perceive no problem with them. As a newbie seeing the game through fresh eyes, however, I can affirm that these are areas for improvement.
-TC