I thought I would just give my initial gut reaction to the 4.0 version I just downloaded.
I am not a image/picture guru in any way and only have limited experience with previous versions, Instead I'm a windows software developer and has been so for 20+ years so I know what happens when you are involved in a project and I know you tend to get "blind" for some of the stuff a new user might seem find confusing or unclear.
So please don't take this as negative criticism and instead just the opinions of a non-graphic-windows-developer.
(well, OK, the moving of the cursor is rally criticism, that's really passing the line )
Couldn't find Options/Settings With an "old" menu like the one in 4.0 I would expect Options to be on the tools menu...but there where not even a tools menu!, so I looked on the edit menu where it used to be way back...but not there either...and not in the files menu...Then I found it way off to the right. All commands/options should be accessible from the menus, putting settings like that on the right will confuse a lot of people. I can not reach Settings with only the keyboard, a big no-no in my book. Always try to do stuff the way people expect them to work, use "The Principle of least astonishment" whenever possible.
MDI/SDI and Multiple images It took me a while to figure out what the little "stamp" in the menu was. Traditionally working with more than one file in windows was handled by just starting a new instance of the program and that was it. Later on MDI (Multi Document Interface) was introduced and let you have sub-windows within your main window, where each window could could be a new document (or a different view the same document, or combinations). The previous version where now referred to as Single Document Interface (SDI). Later versions of for example Office moved away from the MDI approach since it was too "advanced" for "normal" users and kind of went back to the SDI approach, where it now looks like there are, for example, many instances of MS Word running when you have several documents open. Modern Windows now groups the same program under one "button" in the taskbar and lets the user see the content of the different "instances" by hovering over them. The way this is doen in Paint.net 4.0 is compleatly new and does not resemble anything I have seen before. So in my opinion, there has to be a very, VERY good reason to go and do something that is so completely different from everything else. Because when you do this users will be frustrated when they for example, cannot put one image on one their left screen and another one on their right screen. Or why they don't see the different open images when they hover over the taskbar as they kind of do for any other program they have installed. And even though the application displays a good overview of opened images when you hover over the taskbar, you don't get a similar functionality with the classical ALT+TAB which many users use since it gives a very good overview of all opened documents. So picking a completely new way to do something that has evolved since the late 80-ies is a big responsibility.
The Settings Dialog First, never ever move my cursor (mouse-pointer)!!! There is a mouse-setting in the control-panel in windows to position the cursor over the default button in a dialog. Users will use that if they want their cursor moved. The cursor position is READ_ONLY!! User Interface Perhaps an explanation in a tooltip what the different checkboxes actually do, and why you would want to select/not select an option. Tools "tab" The flowing-layout needs to know which elements belong together so that it moves all the stuff to a new line as a unit. As it is now it can be very hard to understand/see how different things in there relate to each other. Perhaps one setting should always be on a line of it's own to remove any confusion on what label/setting (or part of a setting) belongs to what.
No Gamma levels? I couldn't find any way of changing what I believe is called Gamma (again, not a graphing/photo editor)...perhaps it is in one of the curves or levels tools....but I am not really sure how to use them....a gamma level modification tool (like setting gamma in a game) would be good I think.
Text Perhaps this is by design, but when I wrote text it kind of become one with the picture, and I couldn't move it around...like it does in MS Paint...I guess I am doing something wrong because I can't see why I wouldn't want to select the text afterwards and perhaps move it or change the font or whatever...
Selection At some point I managed to get some kind of rectangular selection and it started living it's own life. I never understood how it worked...I could move it around, rotate it and stuff...even move it outside the picture...perhaps this is correct and would be perfectly good/obvious for someone working with graphics....but when I move a selection in Word or Excel the data kind of follows....not just the area of the selection.....it seemed strange....but again, I'm a developer...
View - Menu Can't find a way to hide or show the different utility windows, like the history or the toolbox....why they are not here I can't understand. By only having them as "strange" buttons to the right, again, makes it impossible to turn them on/off by use of the standard way to interact with the menu in Windows.
OK, I'm sure I am missing a lot and that some of this will be understood when I click around a bit more....this is my initial impression after using 4.0 for 10 minutes.