I don’t really like the color (too bright for my taste), but i can bare it. But those buttons, especially the red close button. I do like, that you have removed those buttons i never use.
Btw, in your screenshot Bookmarks are also before the Actions menu. Is it intended?
Coming from the older versions most users will be used to have Actions menu before the bookmarks. Not a big deal, of course. I use my bookmarks rarely and i use broadcasting option quite often.
In the recent builds Spark’s systray icon looks worse comparing to taskbar window icon or shortcut icon. Red sparkle inside the yellow one has jagged edges.
With the given statment above (trying to make it look like 2.5.8) it looks good to me. I still don’t like the colapisble window starting with the same color as the background and ending with white. I would either reverse this (start with white and end with the background color) or preferably start with a slightly darker color and end with the same color as the background to give a little more feeling of seperation to the colapisble menus. I will admit, I don’t remember if this was in 2.5.8 or not.
An enhancment might be to just add this as an option in the default.prefs and Appearance/Colors menu.