Obviously it's not just applicable to Perfect Dark - the last time I really played split screen was when I got together with some old roommates before one of their weddings and we played some good old fashioned Halo: CE (sometime after Halo 2, before Halo 3).  Part of the joy of it is the nostalgia factor, but really you forget what's been lost since seemingly all co-op is done over the net nowadays.
 
I had my brother over last weekend and we played Perfect Dark for an hour or so, something we used to do on the N64 back when it first came out.  We were doing some of the challenges in the combat simulator together and I have to say, it was a blast.  It's just so much easier for me to talk to someone sitting next to me than over a damn headset.  That's sometime I've just never gotten used to.  I don't know why - it seems like it would be close to the same, but it's much better for my teamwork ability when they're sitting next to me on the couch. 
 
Just thought I'd gush again about how much this game was worth the dollars spent.  Still love it,  single player and the shooting range, too.