Well there's a few things, given Black Metal has various kinds of expression...
Honesty. Sounds like a wierd thing to say, but musical honesty. I don't want over the top stuff for over the top's sake, it must be legitimate. Lies and art do not mix.
Technical proficiency is irrelevant, thoughtful and effective songwriting is. If there is technical proficiency in the music, then great, but there must be a good song to back it up.
Intelligent lyrics, where possible. Well researched themes (see Deathspell Omega, great example).
For Pagan Black Metal as an example, I want ethnic influences on the music and lyrics. History, ethnic instruments, culture. You name it. Black Metal is an excellent modern ethnic expression.
Fuck English - it is a generally pathetic language for music anyway (one need only look at how much better an opera sounds when sung in German, Italian or French as opposed to English). English has horrible aural structures for singing imo.
For Satanic Black Metal, I would like to see more Latin based recital, more references to biblical things.
I guess really, as the first point implied, I want legitimacy in my Black Metal. When it's used for posing, it is crippled. but when legitimately and intelligently executed, it is the most powerful kind of Metal there is.
To me, Black Metal expression is powerful expression. It must stay true to this via intelligence.