I've been playing around with the Neptune theme in a fairly complex application
with multiple windows, everyone has their own opinion on this type of stuff,
but for what its worth - my take was:-
1. I think the title bar on windows is too deep. It looks good, but if your user has a 1280x1024 window display its taking up a lot of realestate. If you have multiple windows, it becomes an issue I think.
2. The tabs dont really work. When you have a docked tab panel, they appear as blocks above the panel and its not really clear what they are ie there is no visual hint that they are a tab. Perhaps some shaping on the tab might help?
3. Menus seem messed up. Icons overlap text, they also look a bit narrow and squashed. Same with combo box pull downs.
4. What's happening with the window widgets? They seem OK on webkit but not on FF, etc. Are these CSS3 shaped?
Are there any plans to finish Neptune as a theme?
Personally I'd like to see something even flatter in terms of look and feel, ie almost monochrome, but with the option of some color but that's just me
I know Neptune is under construction at the moment, and it updated with each release. The best thing I can suggest is to create a bug report with screens that display the problem and we will continue to make updates.