I wish I could choose a language to preview the schemes with. My biggest gripe with many of these themes is that is looks great in some languages and terrible for everything else.
Slightly related, I don't like (mostly in OOP langs) when I have something like: import lang.native.api.Something; import third.party.api.Else; ...and syntax file goes to colorize Something , but Else is perceived as common text. I'm aware of limitations of vim, being text editor and not an IDE, but I'd rather syntax file to ignore the native API then to have me draw visual distinction between native and third-party…
You can also quite easily customise syntax highlighting by placing your own additional syntax file in .vim/after/syntax for a language. I use this to add some more custom keywords. You could quite easily add highlight support for ".Else" in an after/syntax file.