I'm a 0L, so take this with a grain of salt, but I work at WilmerHale as a paralegal (V21, I know, so not exactly in the parameters of this thread), and I think the culture is pretty laid-back here (maybe because it's a Boston/DC firm instead of a NYC one?). No one really ever yells, most of the attorneys are grateful and polite, and people seem to have a good sense of humor here. I work on a large case with 50+ lawyers on it, so I have a good bit of experience with the attorneys here.
That being said, I think the lawyers usually keep to themselves pretty much and probably don't go out for many happy hours or drinks after work, from what I can see. The hours are tough, but I don't think they are as bad as some people make it out to be (perhaps NYC firms are worse). Overall, I think WH would be a pretty good firm for a recent law school grad to work at. I know one attorney here left work at Sullivan & Cromwell, because she said the people there were mean and yelled a lot, and has liked it a lot better here.