As I mentioned in another OT thread I think that a lot of Casual RPs technically fall into the Advanced category as far as post length and character/plot development so while I mostly RP in Casual I usually end up with a group of players who would easily qualify for advanced, but I feel like a lot of good RPers are intimidated by the "Advanced" roleplays and play it safe by sticking to "high casual".

What I look for most when I'm GMing (and what I try to do in other RPs I participate in) is player collaboration, especially in the area of developing character relationships (too often there's that one awkward character who can't seem to make any connections) and since roleplay is pretty character-driven in general I think it's really healthy for the game overall. 

One thing I like to do when it comes to accepting characters: I'll give the interested players a CS and have them PM their character(s) to me [i]first[/i], and not posting it in the character thread until I've approved it. Just something I like to do, I think it promotes individuality since no one gets to see each others' characters until I say. It even works in RPs where certain roles need to be filled in the cast. Also, it gives you an opportunity to critique the characters privately and no one suffers the embarrassment of being turned away after posting their character for everyone to see.  

I expect people to put effort into developing the story and their characters, as long as they can do that with quality writing skills post length doesn't really matter to me.