On all known operating systems, widgets are divided into easy to differentiate categories : buttons, checkboxes, radio buttons, etc. and the look for each of these is now pretty much standard, so whenever you see a component you know right ahead how the widget will behave.

What annoys me a lot in blender is that buttons, radio buttons and checkboxes just all look like buttons. So, when looking at a pane you have never seen before, you do not know what widget each button behaves like. Worse, in the case of radio buttons, you do not know how they are grouped. Sometimes you can select one option on each line. Sometimes you can select only one option in the entire bunch. Sometimes they're actually checkboxes and you can check anyway and as many as you wish. etc... it's not predictable.

I agree that once you know the user interface, this is no problem anymore. So long-time users will probably not see much of a problem there. But I think that the interface could be signifcantly easier to learn for beginners (and even long-time users when a new feature is added) if widgets' behaviour was predictable from their looks.

Actually, this might be done as a theme, so people who like the current theme could keep it.

I would like to have an improved file dialog in blender.

rationale :

the current one...
1) does not have my shortcuts (favorite locations)
2) does not display previews and file information like the native one can (for all types of files, not only images)
3) does not use the same icon scheme as my system, therefore I need to read the file extensions and it takes longer (minor)
4) pops up in any window, apparently randomly; sometimes it pops up in e.g. buttons window, where it is way too small to be usable. I then need to use the hotkey to maximize it, then hit the hotkey to minize it after i'm done. this totally defeats the purpose of non-overlapping windows anyway
5) is very grey ;)
6) cannot follow symlinks/aliases on my system