I'm the sort of beta reader who just loves to read, and believes that fanfiction is one of the purest expressions of a person's love for a series.
I am also of the opinion that if you truly love the story that you are writing, it will show through and other people will become enthused with what you have to say.
I am a reader who expects her writers to know his or her characters very very well. I like to ask questions about a story, to help flesh out my understanding of your writing. Even if you're not necessarily going to put that information in the tale, it will broaden my scope, and more likely than not, my enjoyment. Although, if you give me info that you weren't planning on using/don't have an answer to a question and it's necessary for the story, I will let you know.
I am also the type of reader who loves clear descriptions of scenes and characters and what-have-you, and the type of editor who is skilled at paring down purple prose or fleshing out skeletons.
If there is a section I think could be written better, then I will tell you what I find is incorrect (for lack of a better word), and I will give some ideas, but I will not tell you what to write. This is your story, so writing it is your job. I can be brutal if necessary, as I feel that making a story as great as it can be is no easy process, but if you would prefer me to go light, just ask and I will cushion my blows. Quite often I'm not nearly as strict as I tell people I can be, because the stories are more often than not quite good, for the most part, and I see no need to be a hardasp if it isn't necessary. Also, aside from editing the story itself, I put my opinions of the chapter or what-have-you at the end in a sort of review.

My strengths are fixing grammar, mechanics, and helping stories to flow smoothly. Yes, there is a difference between grammar and mechanics. I am quite good at fleshing out and cleaning up descriptions.
I also have a very wide vocabulary, and try my hardest to avoid repetition.

I have a bit of a habit of overusing parentheses, which I am working on fixing.

I prefer drama stories, particularly those of the Hurt/Comfort genre.
I also enjoy romance of almost any flavor-see dislikes for clarification-be it humorous, or slash, or even lemons.
Almost any fandom is welcome. If I do not know the fandom you are writing in, I will look up the story's plot line, then send you a message asking for a synopsis from your point of view. This is to ensure that I understand where you are coming from.

I greatly enjoy humor, but I do not, in any sense of the word, enjoy reading crackfics. If the thread of your story is "I did it for the lulz," please leave me in peace.
I do not like to read yuri or Shojou-ai. I will read it, however, if you make an exceptional case for your story. Likewise with incest.
"Chatspeak" is unacceptable outside of the chatroom. No exceptions.

Cartoon Avatar: Last Airbender

Comic Sandman

General Romance Humor Drama

Poetry Adventure Parody Angst

Suspense Spiritual Family Hurt/Comfort

Friendship