It looks a bit different and it seems to have they own wait cursor i have not seem before.
It seems the "fusion" style is the default, instead of "GTK+".
I would prefer that the default style is the one that the other programs use, so in GNOME maybe GTK+ is the default so i would prefer that to be the default in SMPlayer so check boxes and so on look the same as in other applications.
And i see some buttons are not translated in Qt5 that was translated in Qt4, so maybe people should make sure that Qt5 is well translated in they're language.
I reported some bugs that your told was not there in Qt5 so i will be happy to see them gone.
I notice the About dialog have a scroll bar in the Info tab that give me the possiblity to scroll 1 pixel up or down. Maybe check if there are scroll bars other places that was not there before.