TL;DR
What the heck did I just research? I forget!

What ?
When research is completed, in addition to a sound, have an animation/notification to show what was just unlocked. In addition, make it easy to find recently-unlocked research, perhaps in historical order.

Why ?
I frequently get a bit ...

Had my wife play the tutorial! Wrote up a whole lot of notes. I tried to not give her any feedback, just let her talk it through and figure it out.

Chronologically:

On the very first inventory screen, there are little popups "This area does X <TAB>" "This area does Y <TAB>". She thought it was ...

I have not played thousands of hours like some people here. I've only launched a couple rockets, and I enjoy playing multiplayer with friends. I also haven't played in a while so it's possible things work a bit differently than they did when I played last.

That said, I always assumed that a ...

Ah, great! I had searched but must not have used the right terms. Looks like siggboy's response to that thread is much the same as my suggestion.

I believe the hotbar entries should be shortcuts to items in your inventory, as opposed to being themselves slots to house items.

Here's the issue: if I have 20 of a thing in my inventory, and 50 of them on my hotbar, it's really hard to tell that I actually have 70 of that thing available ...