It's honestly more image based than anything else. There's no real discussion - sometimes there'll be a meta post but they're pretty rare. I've basically linked to a couple of rec blogs and then a bunch of people I know from LJ and I'm still wading through the same 5 gif sets each day most of the time. Heh. I tried searching through tags and it was pretty much impossible because people will tag all sorts of ways too. You can track one particular tag but you'll still end up with about 80% repetition and gifs. I have found the particular tumblrs for a couple of shows and while it's still image based, there is also news and set photos which is good.

Maybe link to a couple of people you know and are comfortable from LJ and ask for a couple of blog recs for particular fandoms to start off.

I think there's more fandom discussion on Twitter although that's the last social network thingie that I'm resisting. :)