Personally I love long meaningful posts, especially in the first post. I enjoy being able to read more about the what is to take place and what the general feel of the roleplay is going to be like because you can't always get that in the OOC. Sure, if it's line after line of utter crap that is a no-go for me but I like reading more about the background and having things established within the OP so that when I start to write out my post I know what I am doing.

However I have a feeling that I am not in the majority here. Long posts can make people uneasy especially if they think they have to reciprocate the post with something equally as long. Not only that, a post that is more dense and longer is going to take more time to read and process the post to figure what all is happening and what exactly the OP is trying to portray. One thing that I've seen that helps with this is gradually introduce more information so that if the roleplay is capable of doing so, have the background information span over the first few posts so that they roleplayers can have manageable post size to digest instead of some monstrous sized post slapping them in the face when they check and see the first post.