As I see it, redditors in general are:

• friendly, supportive and sometimes generous when their sense of community or pity is provoked;
• not infrequently nasty when they disagree over something important to their sense of identity, like politics or taste in music;
• negative about and pessimistic towards the perceived enemies of liberals (including Fox News, Republicans, corporations, and Christianity), and sometimes towards the perceived enemies of male introverts [1] (including women and socially successful men).

There's been somewhat more pessimism about economic matters in the last year, which I'm guessing is due to a combination of the financial crisis and media coverage about the financial crisis. Also, being mostly liberal, there's been extra pessimism about politics because of disillusionment with Obama, adding to the already-existing pessimism about politics that occurs because redditors, despite being broadly liberal, tend to like hopeless fringe political movements and candidates like drug legalization [2], Dennis Kucinich and Ron Paul).

1. Edit: As lucidfox pointed out, the term "male introverts" was poorly chosen. It's not a very accurate descriptor for the category I was trying to point to. I am a male introvert myself, and I'm as socially successful as I currently care to be. But I think the cluster I meant is fairly well-known - bitter, socially inept faux-Nice Guys with entitlement problems. Reddit has an unusual density of those guys.

2. Edit: I agree with NancyLebowitz's caveat: drug legalization is a viable long-term goal. But it's a dispiriting cause in the short-term.